mirror of
https://github.com/google/snappy.git
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2327 lines
85 KiB
C++
2327 lines
85 KiB
C++
// Copyright 2005 Google Inc. All Rights Reserved.
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//
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// Redistribution and use in source and binary forms, with or without
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// modification, are permitted provided that the following conditions are
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// met:
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//
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// * Redistributions of source code must retain the above copyright
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// notice, this list of conditions and the following disclaimer.
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// * Redistributions in binary form must reproduce the above
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// copyright notice, this list of conditions and the following disclaimer
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// in the documentation and/or other materials provided with the
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// distribution.
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// * Neither the name of Google Inc. nor the names of its
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// contributors may be used to endorse or promote products derived from
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// this software without specific prior written permission.
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//
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// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
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// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
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// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
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// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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#include "snappy-internal.h"
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#include "snappy-sinksource.h"
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#include "snappy.h"
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#if !defined(SNAPPY_HAVE_BMI2)
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// __BMI2__ is defined by GCC and Clang. Visual Studio doesn't target BMI2
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// specifically, but it does define __AVX2__ when AVX2 support is available.
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// Fortunately, AVX2 was introduced in Haswell, just like BMI2.
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//
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// BMI2 is not defined as a subset of AVX2 (unlike SSSE3 and AVX above). So,
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// GCC and Clang can build code with AVX2 enabled but BMI2 disabled, in which
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// case issuing BMI2 instructions results in a compiler error.
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#if defined(__BMI2__) || (defined(_MSC_VER) && defined(__AVX2__))
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#define SNAPPY_HAVE_BMI2 1
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#else
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#define SNAPPY_HAVE_BMI2 0
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#endif
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#endif // !defined(SNAPPY_HAVE_BMI2)
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#if SNAPPY_HAVE_BMI2
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// Please do not replace with <x86intrin.h>. or with headers that assume more
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// advanced SSE versions without checking with all the OWNERS.
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#include <immintrin.h>
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#endif
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#include <algorithm>
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#include <array>
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#include <cstddef>
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#include <cstdint>
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#include <cstdio>
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#include <cstring>
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#include <string>
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#include <utility>
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#include <vector>
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namespace snappy {
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namespace {
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// The amount of slop bytes writers are using for unconditional copies.
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constexpr int kSlopBytes = 64;
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using internal::char_table;
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using internal::COPY_1_BYTE_OFFSET;
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using internal::COPY_2_BYTE_OFFSET;
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using internal::COPY_4_BYTE_OFFSET;
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using internal::kMaximumTagLength;
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using internal::LITERAL;
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#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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using internal::V128;
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using internal::V128_Load;
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using internal::V128_LoadU;
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using internal::V128_Shuffle;
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using internal::V128_StoreU;
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using internal::V128_DupChar;
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#endif
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// We translate the information encoded in a tag through a lookup table to a
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// format that requires fewer instructions to decode. Effectively we store
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// the length minus the tag part of the offset. The lowest significant byte
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// thus stores the length. While total length - offset is given by
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// entry - ExtractOffset(type). The nice thing is that the subtraction
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// immediately sets the flags for the necessary check that offset >= length.
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// This folds the cmp with sub. We engineer the long literals and copy-4 to
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// always fail this check, so their presence doesn't affect the fast path.
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// To prevent literals from triggering the guard against offset < length (offset
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// does not apply to literals) the table is giving them a spurious offset of
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// 256.
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inline constexpr int16_t MakeEntry(int16_t len, int16_t offset) {
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return len - (offset << 8);
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}
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inline constexpr int16_t LengthMinusOffset(int data, int type) {
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return type == 3 ? 0xFF // copy-4 (or type == 3)
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: type == 2 ? MakeEntry(data + 1, 0) // copy-2
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: type == 1 ? MakeEntry((data & 7) + 4, data >> 3) // copy-1
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: data < 60 ? MakeEntry(data + 1, 1) // note spurious offset.
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: 0xFF; // long literal
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}
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inline constexpr int16_t LengthMinusOffset(uint8_t tag) {
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return LengthMinusOffset(tag >> 2, tag & 3);
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}
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template <size_t... Ints>
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struct index_sequence {};
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template <std::size_t N, size_t... Is>
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struct make_index_sequence : make_index_sequence<N - 1, N - 1, Is...> {};
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template <size_t... Is>
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struct make_index_sequence<0, Is...> : index_sequence<Is...> {};
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template <size_t... seq>
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constexpr std::array<int16_t, 256> MakeTable(index_sequence<seq...>) {
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return std::array<int16_t, 256>{LengthMinusOffset(seq)...};
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}
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alignas(64) const std::array<int16_t, 256> kLengthMinusOffset =
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MakeTable(make_index_sequence<256>{});
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// Any hash function will produce a valid compressed bitstream, but a good
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// hash function reduces the number of collisions and thus yields better
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// compression for compressible input, and more speed for incompressible
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// input. Of course, it doesn't hurt if the hash function is reasonably fast
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// either, as it gets called a lot.
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inline uint32_t HashBytes(uint32_t bytes, uint32_t mask) {
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constexpr uint32_t kMagic = 0x1e35a7bd;
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return ((kMagic * bytes) >> (32 - kMaxHashTableBits)) & mask;
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}
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} // namespace
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size_t MaxCompressedLength(size_t source_bytes) {
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// Compressed data can be defined as:
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// compressed := item* literal*
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// item := literal* copy
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//
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// The trailing literal sequence has a space blowup of at most 62/60
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// since a literal of length 60 needs one tag byte + one extra byte
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// for length information.
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//
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// Item blowup is trickier to measure. Suppose the "copy" op copies
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// 4 bytes of data. Because of a special check in the encoding code,
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// we produce a 4-byte copy only if the offset is < 65536. Therefore
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// the copy op takes 3 bytes to encode, and this type of item leads
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// to at most the 62/60 blowup for representing literals.
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//
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// Suppose the "copy" op copies 5 bytes of data. If the offset is big
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// enough, it will take 5 bytes to encode the copy op. Therefore the
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// worst case here is a one-byte literal followed by a five-byte copy.
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// I.e., 6 bytes of input turn into 7 bytes of "compressed" data.
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//
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// This last factor dominates the blowup, so the final estimate is:
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return 32 + source_bytes + source_bytes / 6;
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}
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namespace {
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void UnalignedCopy64(const void* src, void* dst) {
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char tmp[8];
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std::memcpy(tmp, src, 8);
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std::memcpy(dst, tmp, 8);
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}
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void UnalignedCopy128(const void* src, void* dst) {
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// std::memcpy() gets vectorized when the appropriate compiler options are
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// used. For example, x86 compilers targeting SSE2+ will optimize to an SSE2
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// load and store.
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char tmp[16];
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std::memcpy(tmp, src, 16);
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std::memcpy(dst, tmp, 16);
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}
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template <bool use_16bytes_chunk>
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inline void ConditionalUnalignedCopy128(const char* src, char* dst) {
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if (use_16bytes_chunk) {
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UnalignedCopy128(src, dst);
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} else {
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UnalignedCopy64(src, dst);
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UnalignedCopy64(src + 8, dst + 8);
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}
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}
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// Copy [src, src+(op_limit-op)) to [op, (op_limit-op)) a byte at a time. Used
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// for handling COPY operations where the input and output regions may overlap.
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// For example, suppose:
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// src == "ab"
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// op == src + 2
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// op_limit == op + 20
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// After IncrementalCopySlow(src, op, op_limit), the result will have eleven
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// copies of "ab"
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// ababababababababababab
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// Note that this does not match the semantics of either std::memcpy() or
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// std::memmove().
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inline char* IncrementalCopySlow(const char* src, char* op,
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char* const op_limit) {
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// TODO: Remove pragma when LLVM is aware this
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// function is only called in cold regions and when cold regions don't get
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// vectorized or unrolled.
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#ifdef __clang__
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#pragma clang loop unroll(disable)
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#endif
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while (op < op_limit) {
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*op++ = *src++;
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}
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return op_limit;
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}
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#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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// Computes the bytes for shuffle control mask (please read comments on
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// 'pattern_generation_masks' as well) for the given index_offset and
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// pattern_size. For example, when the 'offset' is 6, it will generate a
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// repeating pattern of size 6. So, the first 16 byte indexes will correspond to
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// the pattern-bytes {0, 1, 2, 3, 4, 5, 0, 1, 2, 3, 4, 5, 0, 1, 2, 3} and the
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// next 16 byte indexes will correspond to the pattern-bytes {4, 5, 0, 1, 2, 3,
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// 4, 5, 0, 1, 2, 3, 4, 5, 0, 1}. These byte index sequences are generated by
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// calling MakePatternMaskBytes(0, 6, index_sequence<16>()) and
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// MakePatternMaskBytes(16, 6, index_sequence<16>()) respectively.
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template <size_t... indexes>
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inline constexpr std::array<char, sizeof...(indexes)> MakePatternMaskBytes(
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int index_offset, int pattern_size, index_sequence<indexes...>) {
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return {static_cast<char>((index_offset + indexes) % pattern_size)...};
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}
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// Computes the shuffle control mask bytes array for given pattern-sizes and
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// returns an array.
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template <size_t... pattern_sizes_minus_one>
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inline constexpr std::array<std::array<char, sizeof(V128)>,
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sizeof...(pattern_sizes_minus_one)>
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MakePatternMaskBytesTable(int index_offset,
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index_sequence<pattern_sizes_minus_one...>) {
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return {
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MakePatternMaskBytes(index_offset, pattern_sizes_minus_one + 1,
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make_index_sequence</*indexes=*/sizeof(V128)>())...};
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}
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// This is an array of shuffle control masks that can be used as the source
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// operand for PSHUFB to permute the contents of the destination XMM register
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// into a repeating byte pattern.
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alignas(16) constexpr std::array<std::array<char, sizeof(V128)>,
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16> pattern_generation_masks =
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MakePatternMaskBytesTable(
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/*index_offset=*/0,
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/*pattern_sizes_minus_one=*/make_index_sequence<16>());
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// Similar to 'pattern_generation_masks', this table is used to "rotate" the
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// pattern so that we can copy the *next 16 bytes* consistent with the pattern.
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// Basically, pattern_reshuffle_masks is a continuation of
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// pattern_generation_masks. It follows that, pattern_reshuffle_masks is same as
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// pattern_generation_masks for offsets 1, 2, 4, 8 and 16.
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alignas(16) constexpr std::array<std::array<char, sizeof(V128)>,
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16> pattern_reshuffle_masks =
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MakePatternMaskBytesTable(
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/*index_offset=*/16,
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/*pattern_sizes_minus_one=*/make_index_sequence<16>());
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SNAPPY_ATTRIBUTE_ALWAYS_INLINE
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static inline V128 LoadPattern(const char* src, const size_t pattern_size) {
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V128 generation_mask = V128_Load(reinterpret_cast<const V128*>(
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pattern_generation_masks[pattern_size - 1].data()));
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// Uninitialized bytes are masked out by the shuffle mask.
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// TODO: remove annotation and macro defs once MSan is fixed.
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SNAPPY_ANNOTATE_MEMORY_IS_INITIALIZED(src + pattern_size, 16 - pattern_size);
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return V128_Shuffle(V128_LoadU(reinterpret_cast<const V128*>(src)),
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generation_mask);
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}
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SNAPPY_ATTRIBUTE_ALWAYS_INLINE
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static inline std::pair<V128 /* pattern */, V128 /* reshuffle_mask */>
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LoadPatternAndReshuffleMask(const char* src, const size_t pattern_size) {
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V128 pattern = LoadPattern(src, pattern_size);
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// This mask will generate the next 16 bytes in-place. Doing so enables us to
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// write data by at most 4 V128_StoreU.
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//
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// For example, suppose pattern is: abcdefabcdefabcd
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// Shuffling with this mask will generate: efabcdefabcdefab
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// Shuffling again will generate: cdefabcdefabcdef
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V128 reshuffle_mask = V128_Load(reinterpret_cast<const V128*>(
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pattern_reshuffle_masks[pattern_size - 1].data()));
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return {pattern, reshuffle_mask};
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}
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#endif // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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// Fallback for when we need to copy while extending the pattern, for example
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// copying 10 bytes from 3 positions back abc -> abcabcabcabca.
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//
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// REQUIRES: [dst - offset, dst + 64) is a valid address range.
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SNAPPY_ATTRIBUTE_ALWAYS_INLINE
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static inline bool Copy64BytesWithPatternExtension(char* dst, size_t offset) {
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#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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if (SNAPPY_PREDICT_TRUE(offset <= 16)) {
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switch (offset) {
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case 0:
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return false;
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case 1: {
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// TODO: Ideally we should memset, move back once the
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// codegen issues are fixed.
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V128 pattern = V128_DupChar(dst[-1]);
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for (int i = 0; i < 4; i++) {
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V128_StoreU(reinterpret_cast<V128*>(dst + 16 * i), pattern);
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}
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return true;
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}
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case 2:
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case 4:
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case 8:
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case 16: {
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V128 pattern = LoadPattern(dst - offset, offset);
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for (int i = 0; i < 4; i++) {
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V128_StoreU(reinterpret_cast<V128*>(dst + 16 * i), pattern);
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}
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return true;
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}
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default: {
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auto pattern_and_reshuffle_mask =
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LoadPatternAndReshuffleMask(dst - offset, offset);
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V128 pattern = pattern_and_reshuffle_mask.first;
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V128 reshuffle_mask = pattern_and_reshuffle_mask.second;
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for (int i = 0; i < 4; i++) {
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V128_StoreU(reinterpret_cast<V128*>(dst + 16 * i), pattern);
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pattern = V128_Shuffle(pattern, reshuffle_mask);
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}
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return true;
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}
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}
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}
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#else
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if (SNAPPY_PREDICT_TRUE(offset < 16)) {
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if (SNAPPY_PREDICT_FALSE(offset == 0)) return false;
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// Extend the pattern to the first 16 bytes.
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// The simpler formulation of `dst[i - offset]` induces undefined behavior.
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for (int i = 0; i < 16; i++) dst[i] = (dst - offset)[i];
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// Find a multiple of pattern >= 16.
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static std::array<uint8_t, 16> pattern_sizes = []() {
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std::array<uint8_t, 16> res;
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for (int i = 1; i < 16; i++) res[i] = (16 / i + 1) * i;
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return res;
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}();
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offset = pattern_sizes[offset];
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for (int i = 1; i < 4; i++) {
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std::memcpy(dst + i * 16, dst + i * 16 - offset, 16);
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}
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return true;
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}
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#endif // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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// Very rare.
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for (int i = 0; i < 4; i++) {
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std::memcpy(dst + i * 16, dst + i * 16 - offset, 16);
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}
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return true;
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}
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// Copy [src, src+(op_limit-op)) to [op, op_limit) but faster than
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// IncrementalCopySlow. buf_limit is the address past the end of the writable
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// region of the buffer.
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inline char* IncrementalCopy(const char* src, char* op, char* const op_limit,
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char* const buf_limit) {
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#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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constexpr int big_pattern_size_lower_bound = 16;
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#else
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constexpr int big_pattern_size_lower_bound = 8;
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#endif
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// Terminology:
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//
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// slop = buf_limit - op
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// pat = op - src
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// len = op_limit - op
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assert(src < op);
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assert(op < op_limit);
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assert(op_limit <= buf_limit);
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// NOTE: The copy tags use 3 or 6 bits to store the copy length, so len <= 64.
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assert(op_limit - op <= 64);
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// NOTE: In practice the compressor always emits len >= 4, so it is ok to
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// assume that to optimize this function, but this is not guaranteed by the
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// compression format, so we have to also handle len < 4 in case the input
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// does not satisfy these conditions.
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size_t pattern_size = op - src;
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// The cases are split into different branches to allow the branch predictor,
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// FDO, and static prediction hints to work better. For each input we list the
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// ratio of invocations that match each condition.
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//
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// input slop < 16 pat < 8 len > 16
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// ------------------------------------------
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// html|html4|cp 0% 1.01% 27.73%
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// urls 0% 0.88% 14.79%
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// jpg 0% 64.29% 7.14%
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// pdf 0% 2.56% 58.06%
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// txt[1-4] 0% 0.23% 0.97%
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// pb 0% 0.96% 13.88%
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// bin 0.01% 22.27% 41.17%
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//
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// It is very rare that we don't have enough slop for doing block copies. It
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// is also rare that we need to expand a pattern. Small patterns are common
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// for incompressible formats and for those we are plenty fast already.
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// Lengths are normally not greater than 16 but they vary depending on the
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// input. In general if we always predict len <= 16 it would be an ok
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// prediction.
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//
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// In order to be fast we want a pattern >= 16 bytes (or 8 bytes in non-SSE)
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// and an unrolled loop copying 1x 16 bytes (or 2x 8 bytes in non-SSE) at a
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// time.
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// Handle the uncommon case where pattern is less than 16 (or 8 in non-SSE)
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// bytes.
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if (pattern_size < big_pattern_size_lower_bound) {
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#if SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
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// Load the first eight bytes into an 128-bit XMM register, then use PSHUFB
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// to permute the register's contents in-place into a repeating sequence of
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// the first "pattern_size" bytes.
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// For example, suppose:
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// src == "abc"
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// op == op + 3
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// After V128_Shuffle(), "pattern" will have five copies of "abc"
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// followed by one byte of slop: abcabcabcabcabca.
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//
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// The non-SSE fallback implementation suffers from store-forwarding stalls
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// because its loads and stores partly overlap. By expanding the pattern
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// in-place, we avoid the penalty.
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// Typically, the op_limit is the gating factor so try to simplify the loop
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// based on that.
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if (SNAPPY_PREDICT_TRUE(op_limit <= buf_limit - 15)) {
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auto pattern_and_reshuffle_mask =
|
|
LoadPatternAndReshuffleMask(src, pattern_size);
|
|
V128 pattern = pattern_and_reshuffle_mask.first;
|
|
V128 reshuffle_mask = pattern_and_reshuffle_mask.second;
|
|
|
|
// There is at least one, and at most four 16-byte blocks. Writing four
|
|
// conditionals instead of a loop allows FDO to layout the code with
|
|
// respect to the actual probabilities of each length.
|
|
// TODO: Replace with loop with trip count hint.
|
|
V128_StoreU(reinterpret_cast<V128*>(op), pattern);
|
|
|
|
if (op + 16 < op_limit) {
|
|
pattern = V128_Shuffle(pattern, reshuffle_mask);
|
|
V128_StoreU(reinterpret_cast<V128*>(op + 16), pattern);
|
|
}
|
|
if (op + 32 < op_limit) {
|
|
pattern = V128_Shuffle(pattern, reshuffle_mask);
|
|
V128_StoreU(reinterpret_cast<V128*>(op + 32), pattern);
|
|
}
|
|
if (op + 48 < op_limit) {
|
|
pattern = V128_Shuffle(pattern, reshuffle_mask);
|
|
V128_StoreU(reinterpret_cast<V128*>(op + 48), pattern);
|
|
}
|
|
return op_limit;
|
|
}
|
|
char* const op_end = buf_limit - 15;
|
|
if (SNAPPY_PREDICT_TRUE(op < op_end)) {
|
|
auto pattern_and_reshuffle_mask =
|
|
LoadPatternAndReshuffleMask(src, pattern_size);
|
|
V128 pattern = pattern_and_reshuffle_mask.first;
|
|
V128 reshuffle_mask = pattern_and_reshuffle_mask.second;
|
|
|
|
// This code path is relatively cold however so we save code size
|
|
// by avoiding unrolling and vectorizing.
|
|
//
|
|
// TODO: Remove pragma when when cold regions don't get
|
|
// vectorized or unrolled.
|
|
#ifdef __clang__
|
|
#pragma clang loop unroll(disable)
|
|
#endif
|
|
do {
|
|
V128_StoreU(reinterpret_cast<V128*>(op), pattern);
|
|
pattern = V128_Shuffle(pattern, reshuffle_mask);
|
|
op += 16;
|
|
} while (SNAPPY_PREDICT_TRUE(op < op_end));
|
|
}
|
|
return IncrementalCopySlow(op - pattern_size, op, op_limit);
|
|
#else // !SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
|
|
// If plenty of buffer space remains, expand the pattern to at least 8
|
|
// bytes. The way the following loop is written, we need 8 bytes of buffer
|
|
// space if pattern_size >= 4, 11 bytes if pattern_size is 1 or 3, and 10
|
|
// bytes if pattern_size is 2. Precisely encoding that is probably not
|
|
// worthwhile; instead, invoke the slow path if we cannot write 11 bytes
|
|
// (because 11 are required in the worst case).
|
|
if (SNAPPY_PREDICT_TRUE(op <= buf_limit - 11)) {
|
|
while (pattern_size < 8) {
|
|
UnalignedCopy64(src, op);
|
|
op += pattern_size;
|
|
pattern_size *= 2;
|
|
}
|
|
if (SNAPPY_PREDICT_TRUE(op >= op_limit)) return op_limit;
|
|
} else {
|
|
return IncrementalCopySlow(src, op, op_limit);
|
|
}
|
|
#endif // SNAPPY_HAVE_VECTOR_BYTE_SHUFFLE
|
|
}
|
|
assert(pattern_size >= big_pattern_size_lower_bound);
|
|
constexpr bool use_16bytes_chunk = big_pattern_size_lower_bound == 16;
|
|
|
|
// Copy 1x 16 bytes (or 2x 8 bytes in non-SSE) at a time. Because op - src can
|
|
// be < 16 in non-SSE, a single UnalignedCopy128 might overwrite data in op.
|
|
// UnalignedCopy64 is safe because expanding the pattern to at least 8 bytes
|
|
// guarantees that op - src >= 8.
|
|
//
|
|
// Typically, the op_limit is the gating factor so try to simplify the loop
|
|
// based on that.
|
|
if (SNAPPY_PREDICT_TRUE(op_limit <= buf_limit - 15)) {
|
|
// There is at least one, and at most four 16-byte blocks. Writing four
|
|
// conditionals instead of a loop allows FDO to layout the code with respect
|
|
// to the actual probabilities of each length.
|
|
// TODO: Replace with loop with trip count hint.
|
|
ConditionalUnalignedCopy128<use_16bytes_chunk>(src, op);
|
|
if (op + 16 < op_limit) {
|
|
ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 16, op + 16);
|
|
}
|
|
if (op + 32 < op_limit) {
|
|
ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 32, op + 32);
|
|
}
|
|
if (op + 48 < op_limit) {
|
|
ConditionalUnalignedCopy128<use_16bytes_chunk>(src + 48, op + 48);
|
|
}
|
|
return op_limit;
|
|
}
|
|
|
|
// Fall back to doing as much as we can with the available slop in the
|
|
// buffer. This code path is relatively cold however so we save code size by
|
|
// avoiding unrolling and vectorizing.
|
|
//
|
|
// TODO: Remove pragma when when cold regions don't get vectorized
|
|
// or unrolled.
|
|
#ifdef __clang__
|
|
#pragma clang loop unroll(disable)
|
|
#endif
|
|
for (char* op_end = buf_limit - 16; op < op_end; op += 16, src += 16) {
|
|
ConditionalUnalignedCopy128<use_16bytes_chunk>(src, op);
|
|
}
|
|
if (op >= op_limit) return op_limit;
|
|
|
|
// We only take this branch if we didn't have enough slop and we can do a
|
|
// single 8 byte copy.
|
|
if (SNAPPY_PREDICT_FALSE(op <= buf_limit - 8)) {
|
|
UnalignedCopy64(src, op);
|
|
src += 8;
|
|
op += 8;
|
|
}
|
|
return IncrementalCopySlow(src, op, op_limit);
|
|
}
|
|
|
|
} // namespace
|
|
|
|
template <bool allow_fast_path>
|
|
static inline char* EmitLiteral(char* op, const char* literal, int len) {
|
|
// The vast majority of copies are below 16 bytes, for which a
|
|
// call to std::memcpy() is overkill. This fast path can sometimes
|
|
// copy up to 15 bytes too much, but that is okay in the
|
|
// main loop, since we have a bit to go on for both sides:
|
|
//
|
|
// - The input will always have kInputMarginBytes = 15 extra
|
|
// available bytes, as long as we're in the main loop, and
|
|
// if not, allow_fast_path = false.
|
|
// - The output will always have 32 spare bytes (see
|
|
// MaxCompressedLength).
|
|
assert(len > 0); // Zero-length literals are disallowed
|
|
int n = len - 1;
|
|
if (allow_fast_path && len <= 16) {
|
|
// Fits in tag byte
|
|
*op++ = LITERAL | (n << 2);
|
|
|
|
UnalignedCopy128(literal, op);
|
|
return op + len;
|
|
}
|
|
|
|
if (n < 60) {
|
|
// Fits in tag byte
|
|
*op++ = LITERAL | (n << 2);
|
|
} else {
|
|
int count = (Bits::Log2Floor(n) >> 3) + 1;
|
|
assert(count >= 1);
|
|
assert(count <= 4);
|
|
*op++ = LITERAL | ((59 + count) << 2);
|
|
// Encode in upcoming bytes.
|
|
// Write 4 bytes, though we may care about only 1 of them. The output buffer
|
|
// is guaranteed to have at least 3 more spaces left as 'len >= 61' holds
|
|
// here and there is a std::memcpy() of size 'len' below.
|
|
LittleEndian::Store32(op, n);
|
|
op += count;
|
|
}
|
|
std::memcpy(op, literal, len);
|
|
return op + len;
|
|
}
|
|
|
|
template <bool len_less_than_12>
|
|
static inline char* EmitCopyAtMost64(char* op, size_t offset, size_t len) {
|
|
assert(len <= 64);
|
|
assert(len >= 4);
|
|
assert(offset < 65536);
|
|
assert(len_less_than_12 == (len < 12));
|
|
|
|
if (len_less_than_12) {
|
|
uint32_t u = (len << 2) + (offset << 8);
|
|
uint32_t copy1 = COPY_1_BYTE_OFFSET - (4 << 2) + ((offset >> 3) & 0xe0);
|
|
uint32_t copy2 = COPY_2_BYTE_OFFSET - (1 << 2);
|
|
// It turns out that offset < 2048 is a difficult to predict branch.
|
|
// `perf record` shows this is the highest percentage of branch misses in
|
|
// benchmarks. This code produces branch free code, the data dependency
|
|
// chain that bottlenecks the throughput is so long that a few extra
|
|
// instructions are completely free (IPC << 6 because of data deps).
|
|
u += offset < 2048 ? copy1 : copy2;
|
|
LittleEndian::Store32(op, u);
|
|
op += offset < 2048 ? 2 : 3;
|
|
} else {
|
|
// Write 4 bytes, though we only care about 3 of them. The output buffer
|
|
// is required to have some slack, so the extra byte won't overrun it.
|
|
uint32_t u = COPY_2_BYTE_OFFSET + ((len - 1) << 2) + (offset << 8);
|
|
LittleEndian::Store32(op, u);
|
|
op += 3;
|
|
}
|
|
return op;
|
|
}
|
|
|
|
template <bool len_less_than_12>
|
|
static inline char* EmitCopy(char* op, size_t offset, size_t len) {
|
|
assert(len_less_than_12 == (len < 12));
|
|
if (len_less_than_12) {
|
|
return EmitCopyAtMost64</*len_less_than_12=*/true>(op, offset, len);
|
|
} else {
|
|
// A special case for len <= 64 might help, but so far measurements suggest
|
|
// it's in the noise.
|
|
|
|
// Emit 64 byte copies but make sure to keep at least four bytes reserved.
|
|
while (SNAPPY_PREDICT_FALSE(len >= 68)) {
|
|
op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, 64);
|
|
len -= 64;
|
|
}
|
|
|
|
// One or two copies will now finish the job.
|
|
if (len > 64) {
|
|
op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, 60);
|
|
len -= 60;
|
|
}
|
|
|
|
// Emit remainder.
|
|
if (len < 12) {
|
|
op = EmitCopyAtMost64</*len_less_than_12=*/true>(op, offset, len);
|
|
} else {
|
|
op = EmitCopyAtMost64</*len_less_than_12=*/false>(op, offset, len);
|
|
}
|
|
return op;
|
|
}
|
|
}
|
|
|
|
bool GetUncompressedLength(const char* start, size_t n, size_t* result) {
|
|
uint32_t v = 0;
|
|
const char* limit = start + n;
|
|
if (Varint::Parse32WithLimit(start, limit, &v) != NULL) {
|
|
*result = v;
|
|
return true;
|
|
} else {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
namespace {
|
|
uint32_t CalculateTableSize(uint32_t input_size) {
|
|
static_assert(
|
|
kMaxHashTableSize >= kMinHashTableSize,
|
|
"kMaxHashTableSize should be greater or equal to kMinHashTableSize.");
|
|
if (input_size > kMaxHashTableSize) {
|
|
return kMaxHashTableSize;
|
|
}
|
|
if (input_size < kMinHashTableSize) {
|
|
return kMinHashTableSize;
|
|
}
|
|
// This is equivalent to Log2Ceiling(input_size), assuming input_size > 1.
|
|
// 2 << Log2Floor(x - 1) is equivalent to 1 << (1 + Log2Floor(x - 1)).
|
|
return 2u << Bits::Log2Floor(input_size - 1);
|
|
}
|
|
} // namespace
|
|
|
|
namespace internal {
|
|
WorkingMemory::WorkingMemory(size_t input_size) {
|
|
const size_t max_fragment_size = std::min(input_size, kBlockSize);
|
|
const size_t table_size = CalculateTableSize(max_fragment_size);
|
|
size_ = table_size * sizeof(*table_) + max_fragment_size +
|
|
MaxCompressedLength(max_fragment_size);
|
|
mem_ = std::allocator<char>().allocate(size_);
|
|
table_ = reinterpret_cast<uint16_t*>(mem_);
|
|
input_ = mem_ + table_size * sizeof(*table_);
|
|
output_ = input_ + max_fragment_size;
|
|
}
|
|
|
|
WorkingMemory::~WorkingMemory() {
|
|
std::allocator<char>().deallocate(mem_, size_);
|
|
}
|
|
|
|
uint16_t* WorkingMemory::GetHashTable(size_t fragment_size,
|
|
int* table_size) const {
|
|
const size_t htsize = CalculateTableSize(fragment_size);
|
|
memset(table_, 0, htsize * sizeof(*table_));
|
|
*table_size = htsize;
|
|
return table_;
|
|
}
|
|
} // end namespace internal
|
|
|
|
// Flat array compression that does not emit the "uncompressed length"
|
|
// prefix. Compresses "input" string to the "*op" buffer.
|
|
//
|
|
// REQUIRES: "input" is at most "kBlockSize" bytes long.
|
|
// REQUIRES: "op" points to an array of memory that is at least
|
|
// "MaxCompressedLength(input.size())" in size.
|
|
// REQUIRES: All elements in "table[0..table_size-1]" are initialized to zero.
|
|
// REQUIRES: "table_size" is a power of two
|
|
//
|
|
// Returns an "end" pointer into "op" buffer.
|
|
// "end - op" is the compressed size of "input".
|
|
namespace internal {
|
|
char* CompressFragment(const char* input, size_t input_size, char* op,
|
|
uint16_t* table, const int table_size) {
|
|
// "ip" is the input pointer, and "op" is the output pointer.
|
|
const char* ip = input;
|
|
assert(input_size <= kBlockSize);
|
|
assert((table_size & (table_size - 1)) == 0); // table must be power of two
|
|
const uint32_t mask = table_size - 1;
|
|
const char* ip_end = input + input_size;
|
|
const char* base_ip = ip;
|
|
|
|
const size_t kInputMarginBytes = 15;
|
|
if (SNAPPY_PREDICT_TRUE(input_size >= kInputMarginBytes)) {
|
|
const char* ip_limit = input + input_size - kInputMarginBytes;
|
|
|
|
for (uint32_t preload = LittleEndian::Load32(ip + 1);;) {
|
|
// Bytes in [next_emit, ip) will be emitted as literal bytes. Or
|
|
// [next_emit, ip_end) after the main loop.
|
|
const char* next_emit = ip++;
|
|
uint64_t data = LittleEndian::Load64(ip);
|
|
// The body of this loop calls EmitLiteral once and then EmitCopy one or
|
|
// more times. (The exception is that when we're close to exhausting
|
|
// the input we goto emit_remainder.)
|
|
//
|
|
// In the first iteration of this loop we're just starting, so
|
|
// there's nothing to copy, so calling EmitLiteral once is
|
|
// necessary. And we only start a new iteration when the
|
|
// current iteration has determined that a call to EmitLiteral will
|
|
// precede the next call to EmitCopy (if any).
|
|
//
|
|
// Step 1: Scan forward in the input looking for a 4-byte-long match.
|
|
// If we get close to exhausting the input then goto emit_remainder.
|
|
//
|
|
// Heuristic match skipping: If 32 bytes are scanned with no matches
|
|
// found, start looking only at every other byte. If 32 more bytes are
|
|
// scanned (or skipped), look at every third byte, etc.. When a match is
|
|
// found, immediately go back to looking at every byte. This is a small
|
|
// loss (~5% performance, ~0.1% density) for compressible data due to more
|
|
// bookkeeping, but for non-compressible data (such as JPEG) it's a huge
|
|
// win since the compressor quickly "realizes" the data is incompressible
|
|
// and doesn't bother looking for matches everywhere.
|
|
//
|
|
// The "skip" variable keeps track of how many bytes there are since the
|
|
// last match; dividing it by 32 (ie. right-shifting by five) gives the
|
|
// number of bytes to move ahead for each iteration.
|
|
uint32_t skip = 32;
|
|
|
|
const char* candidate;
|
|
if (ip_limit - ip >= 16) {
|
|
auto delta = ip - base_ip;
|
|
for (int j = 0; j < 4; ++j) {
|
|
for (int k = 0; k < 4; ++k) {
|
|
int i = 4 * j + k;
|
|
// These for-loops are meant to be unrolled. So we can freely
|
|
// special case the first iteration to use the value already
|
|
// loaded in preload.
|
|
uint32_t dword = i == 0 ? preload : static_cast<uint32_t>(data);
|
|
assert(dword == LittleEndian::Load32(ip + i));
|
|
uint32_t hash = HashBytes(dword, mask);
|
|
candidate = base_ip + table[hash];
|
|
assert(candidate >= base_ip);
|
|
assert(candidate < ip + i);
|
|
table[hash] = delta + i;
|
|
if (SNAPPY_PREDICT_FALSE(LittleEndian::Load32(candidate) == dword)) {
|
|
*op = LITERAL | (i << 2);
|
|
UnalignedCopy128(next_emit, op + 1);
|
|
ip += i;
|
|
op = op + i + 2;
|
|
goto emit_match;
|
|
}
|
|
data >>= 8;
|
|
}
|
|
data = LittleEndian::Load64(ip + 4 * j + 4);
|
|
}
|
|
ip += 16;
|
|
skip += 16;
|
|
}
|
|
while (true) {
|
|
assert(static_cast<uint32_t>(data) == LittleEndian::Load32(ip));
|
|
uint32_t hash = HashBytes(data, mask);
|
|
uint32_t bytes_between_hash_lookups = skip >> 5;
|
|
skip += bytes_between_hash_lookups;
|
|
const char* next_ip = ip + bytes_between_hash_lookups;
|
|
if (SNAPPY_PREDICT_FALSE(next_ip > ip_limit)) {
|
|
ip = next_emit;
|
|
goto emit_remainder;
|
|
}
|
|
candidate = base_ip + table[hash];
|
|
assert(candidate >= base_ip);
|
|
assert(candidate < ip);
|
|
|
|
table[hash] = ip - base_ip;
|
|
if (SNAPPY_PREDICT_FALSE(static_cast<uint32_t>(data) ==
|
|
LittleEndian::Load32(candidate))) {
|
|
break;
|
|
}
|
|
data = LittleEndian::Load32(next_ip);
|
|
ip = next_ip;
|
|
}
|
|
|
|
// Step 2: A 4-byte match has been found. We'll later see if more
|
|
// than 4 bytes match. But, prior to the match, input
|
|
// bytes [next_emit, ip) are unmatched. Emit them as "literal bytes."
|
|
assert(next_emit + 16 <= ip_end);
|
|
op = EmitLiteral</*allow_fast_path=*/true>(op, next_emit, ip - next_emit);
|
|
|
|
// Step 3: Call EmitCopy, and then see if another EmitCopy could
|
|
// be our next move. Repeat until we find no match for the
|
|
// input immediately after what was consumed by the last EmitCopy call.
|
|
//
|
|
// If we exit this loop normally then we need to call EmitLiteral next,
|
|
// though we don't yet know how big the literal will be. We handle that
|
|
// by proceeding to the next iteration of the main loop. We also can exit
|
|
// this loop via goto if we get close to exhausting the input.
|
|
emit_match:
|
|
do {
|
|
// We have a 4-byte match at ip, and no need to emit any
|
|
// "literal bytes" prior to ip.
|
|
const char* base = ip;
|
|
std::pair<size_t, bool> p =
|
|
FindMatchLength(candidate + 4, ip + 4, ip_end, &data);
|
|
size_t matched = 4 + p.first;
|
|
ip += matched;
|
|
size_t offset = base - candidate;
|
|
assert(0 == memcmp(base, candidate, matched));
|
|
if (p.second) {
|
|
op = EmitCopy</*len_less_than_12=*/true>(op, offset, matched);
|
|
} else {
|
|
op = EmitCopy</*len_less_than_12=*/false>(op, offset, matched);
|
|
}
|
|
if (SNAPPY_PREDICT_FALSE(ip >= ip_limit)) {
|
|
goto emit_remainder;
|
|
}
|
|
// Expect 5 bytes to match
|
|
assert((data & 0xFFFFFFFFFF) ==
|
|
(LittleEndian::Load64(ip) & 0xFFFFFFFFFF));
|
|
// We are now looking for a 4-byte match again. We read
|
|
// table[Hash(ip, shift)] for that. To improve compression,
|
|
// we also update table[Hash(ip - 1, mask)] and table[Hash(ip, mask)].
|
|
table[HashBytes(LittleEndian::Load32(ip - 1), mask)] = ip - base_ip - 1;
|
|
uint32_t hash = HashBytes(data, mask);
|
|
candidate = base_ip + table[hash];
|
|
table[hash] = ip - base_ip;
|
|
// Measurements on the benchmarks have shown the following probabilities
|
|
// for the loop to exit (ie. avg. number of iterations is reciprocal).
|
|
// BM_Flat/6 txt1 p = 0.3-0.4
|
|
// BM_Flat/7 txt2 p = 0.35
|
|
// BM_Flat/8 txt3 p = 0.3-0.4
|
|
// BM_Flat/9 txt3 p = 0.34-0.4
|
|
// BM_Flat/10 pb p = 0.4
|
|
// BM_Flat/11 gaviota p = 0.1
|
|
// BM_Flat/12 cp p = 0.5
|
|
// BM_Flat/13 c p = 0.3
|
|
} while (static_cast<uint32_t>(data) == LittleEndian::Load32(candidate));
|
|
// Because the least significant 5 bytes matched, we can utilize data
|
|
// for the next iteration.
|
|
preload = data >> 8;
|
|
}
|
|
}
|
|
|
|
emit_remainder:
|
|
// Emit the remaining bytes as a literal
|
|
if (ip < ip_end) {
|
|
op = EmitLiteral</*allow_fast_path=*/false>(op, ip, ip_end - ip);
|
|
}
|
|
|
|
return op;
|
|
}
|
|
} // end namespace internal
|
|
|
|
// Called back at avery compression call to trace parameters and sizes.
|
|
static inline void Report(const char *algorithm, size_t compressed_size,
|
|
size_t uncompressed_size) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)algorithm;
|
|
(void)compressed_size;
|
|
(void)uncompressed_size;
|
|
}
|
|
|
|
// Signature of output types needed by decompression code.
|
|
// The decompression code is templatized on a type that obeys this
|
|
// signature so that we do not pay virtual function call overhead in
|
|
// the middle of a tight decompression loop.
|
|
//
|
|
// class DecompressionWriter {
|
|
// public:
|
|
// // Called before decompression
|
|
// void SetExpectedLength(size_t length);
|
|
//
|
|
// // For performance a writer may choose to donate the cursor variable to the
|
|
// // decompression function. The decompression will inject it in all its
|
|
// // function calls to the writer. Keeping the important output cursor as a
|
|
// // function local stack variable allows the compiler to keep it in
|
|
// // register, which greatly aids performance by avoiding loads and stores of
|
|
// // this variable in the fast path loop iterations.
|
|
// T GetOutputPtr() const;
|
|
//
|
|
// // At end of decompression the loop donates the ownership of the cursor
|
|
// // variable back to the writer by calling this function.
|
|
// void SetOutputPtr(T op);
|
|
//
|
|
// // Called after decompression
|
|
// bool CheckLength() const;
|
|
//
|
|
// // Called repeatedly during decompression
|
|
// // Each function get a pointer to the op (output pointer), that the writer
|
|
// // can use and update. Note it's important that these functions get fully
|
|
// // inlined so that no actual address of the local variable needs to be
|
|
// // taken.
|
|
// bool Append(const char* ip, size_t length, T* op);
|
|
// bool AppendFromSelf(uint32_t offset, size_t length, T* op);
|
|
//
|
|
// // The rules for how TryFastAppend differs from Append are somewhat
|
|
// // convoluted:
|
|
// //
|
|
// // - TryFastAppend is allowed to decline (return false) at any
|
|
// // time, for any reason -- just "return false" would be
|
|
// // a perfectly legal implementation of TryFastAppend.
|
|
// // The intention is for TryFastAppend to allow a fast path
|
|
// // in the common case of a small append.
|
|
// // - TryFastAppend is allowed to read up to <available> bytes
|
|
// // from the input buffer, whereas Append is allowed to read
|
|
// // <length>. However, if it returns true, it must leave
|
|
// // at least five (kMaximumTagLength) bytes in the input buffer
|
|
// // afterwards, so that there is always enough space to read the
|
|
// // next tag without checking for a refill.
|
|
// // - TryFastAppend must always return decline (return false)
|
|
// // if <length> is 61 or more, as in this case the literal length is not
|
|
// // decoded fully. In practice, this should not be a big problem,
|
|
// // as it is unlikely that one would implement a fast path accepting
|
|
// // this much data.
|
|
// //
|
|
// bool TryFastAppend(const char* ip, size_t available, size_t length, T* op);
|
|
// };
|
|
|
|
static inline uint32_t ExtractLowBytes(const uint32_t& v, int n) {
|
|
assert(n >= 0);
|
|
assert(n <= 4);
|
|
#if SNAPPY_HAVE_BMI2
|
|
return _bzhi_u32(v, 8 * n);
|
|
#else
|
|
// This needs to be wider than uint32_t otherwise `mask << 32` will be
|
|
// undefined.
|
|
uint64_t mask = 0xffffffff;
|
|
return v & ~(mask << (8 * n));
|
|
#endif
|
|
}
|
|
|
|
static inline bool LeftShiftOverflows(uint8_t value, uint32_t shift) {
|
|
assert(shift < 32);
|
|
static const uint8_t masks[] = {
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //
|
|
0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, //
|
|
0x00, 0x80, 0xc0, 0xe0, 0xf0, 0xf8, 0xfc, 0xfe};
|
|
return (value & masks[shift]) != 0;
|
|
}
|
|
|
|
inline bool Copy64BytesWithPatternExtension(ptrdiff_t dst, size_t offset) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)dst;
|
|
return offset != 0;
|
|
}
|
|
|
|
// Copies between size bytes and 64 bytes from src to dest. size cannot exceed
|
|
// 64. More than size bytes, but never exceeding 64, might be copied if doing
|
|
// so gives better performance. [src, src + size) must not overlap with
|
|
// [dst, dst + size), but [src, src + 64) may overlap with [dst, dst + 64).
|
|
void MemCopy64(char* dst, const void* src, size_t size) {
|
|
// Always copy this many bytes, test if we need to copy more.
|
|
constexpr int kShortMemCopy = 32;
|
|
// We're always allowed to copy 64 bytes, so if we exceed kShortMemCopy just
|
|
// copy 64 rather than the exact amount.
|
|
constexpr int kLongMemCopy = 64;
|
|
|
|
assert(size <= kLongMemCopy);
|
|
assert(std::less_equal<const void*>()(static_cast<const char*>(src) + size,
|
|
dst) ||
|
|
std::less_equal<const void*>()(dst + size, src));
|
|
|
|
// We know that src and dst are at least size bytes apart. However, because we
|
|
// might copy more than size bytes the copy still might overlap past size.
|
|
// E.g. if src and dst appear consecutively in memory (src + size == dst).
|
|
std::memmove(dst, src, kShortMemCopy);
|
|
// Profiling shows that nearly all copies are short.
|
|
if (SNAPPY_PREDICT_FALSE(size > kShortMemCopy)) {
|
|
std::memmove(dst + kShortMemCopy,
|
|
static_cast<const uint8_t*>(src) + kShortMemCopy,
|
|
kLongMemCopy - kShortMemCopy);
|
|
}
|
|
}
|
|
|
|
void MemCopy64(ptrdiff_t dst, const void* src, size_t size) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)dst;
|
|
(void)src;
|
|
(void)size;
|
|
}
|
|
|
|
SNAPPY_ATTRIBUTE_ALWAYS_INLINE
|
|
inline size_t AdvanceToNextTagARMOptimized(const uint8_t** ip_p, size_t* tag) {
|
|
const uint8_t*& ip = *ip_p;
|
|
// This section is crucial for the throughput of the decompression loop.
|
|
// The latency of an iteration is fundamentally constrained by the
|
|
// following data chain on ip.
|
|
// ip -> c = Load(ip) -> delta1 = (c & 3) -> ip += delta1 or delta2
|
|
// delta2 = ((c >> 2) + 1) ip++
|
|
// This is different from X86 optimizations because ARM has conditional add
|
|
// instruction (csinc) and it removes several register moves.
|
|
const size_t tag_type = *tag & 3;
|
|
const bool is_literal = (tag_type == 0);
|
|
if (is_literal) {
|
|
size_t next_literal_tag = (*tag >> 2) + 1;
|
|
*tag = ip[next_literal_tag];
|
|
ip += next_literal_tag + 1;
|
|
} else {
|
|
*tag = ip[tag_type];
|
|
ip += tag_type + 1;
|
|
}
|
|
return tag_type;
|
|
}
|
|
|
|
SNAPPY_ATTRIBUTE_ALWAYS_INLINE
|
|
inline size_t AdvanceToNextTagX86Optimized(const uint8_t** ip_p, size_t* tag) {
|
|
const uint8_t*& ip = *ip_p;
|
|
// This section is crucial for the throughput of the decompression loop.
|
|
// The latency of an iteration is fundamentally constrained by the
|
|
// following data chain on ip.
|
|
// ip -> c = Load(ip) -> ip1 = ip + 1 + (c & 3) -> ip = ip1 or ip2
|
|
// ip2 = ip + 2 + (c >> 2)
|
|
// This amounts to 8 cycles.
|
|
// 5 (load) + 1 (c & 3) + 1 (lea ip1, [ip + (c & 3) + 1]) + 1 (cmov)
|
|
size_t literal_len = *tag >> 2;
|
|
size_t tag_type = *tag;
|
|
bool is_literal;
|
|
#if defined(__GCC_ASM_FLAG_OUTPUTS__) && defined(__x86_64__)
|
|
// TODO clang misses the fact that the (c & 3) already correctly
|
|
// sets the zero flag.
|
|
asm("and $3, %k[tag_type]\n\t"
|
|
: [tag_type] "+r"(tag_type), "=@ccz"(is_literal));
|
|
#else
|
|
tag_type &= 3;
|
|
is_literal = (tag_type == 0);
|
|
#endif
|
|
// TODO
|
|
// This is code is subtle. Loading the values first and then cmov has less
|
|
// latency then cmov ip and then load. However clang would move the loads
|
|
// in an optimization phase, volatile prevents this transformation.
|
|
// Note that we have enough slop bytes (64) that the loads are always valid.
|
|
size_t tag_literal =
|
|
static_cast<const volatile uint8_t*>(ip)[1 + literal_len];
|
|
size_t tag_copy = static_cast<const volatile uint8_t*>(ip)[tag_type];
|
|
*tag = is_literal ? tag_literal : tag_copy;
|
|
const uint8_t* ip_copy = ip + 1 + tag_type;
|
|
const uint8_t* ip_literal = ip + 2 + literal_len;
|
|
ip = is_literal ? ip_literal : ip_copy;
|
|
#if defined(__GNUC__) && defined(__x86_64__)
|
|
// TODO Clang is "optimizing" zero-extension (a totally free
|
|
// operation) this means that after the cmov of tag, it emits another movzb
|
|
// tag, byte(tag). It really matters as it's on the core chain. This dummy
|
|
// asm, persuades clang to do the zero-extension at the load (it's automatic)
|
|
// removing the expensive movzb.
|
|
asm("" ::"r"(tag_copy));
|
|
#endif
|
|
return tag_type;
|
|
}
|
|
|
|
// Extract the offset for copy-1 and copy-2 returns 0 for literals or copy-4.
|
|
inline uint32_t ExtractOffset(uint32_t val, size_t tag_type) {
|
|
// For x86 non-static storage works better. For ARM static storage is better.
|
|
// TODO: Once the array is recognized as a register, improve the
|
|
// readability for x86.
|
|
#if defined(__x86_64__)
|
|
constexpr uint64_t kExtractMasksCombined = 0x0000FFFF00FF0000ull;
|
|
uint16_t result;
|
|
memcpy(&result,
|
|
reinterpret_cast<const char*>(&kExtractMasksCombined) + 2 * tag_type,
|
|
sizeof(result));
|
|
return val & result;
|
|
#elif defined(__aarch64__)
|
|
constexpr uint64_t kExtractMasksCombined = 0x0000FFFF00FF0000ull;
|
|
return val & static_cast<uint32_t>(
|
|
(kExtractMasksCombined >> (tag_type * 16)) & 0xFFFF);
|
|
#else
|
|
static constexpr uint32_t kExtractMasks[4] = {0, 0xFF, 0xFFFF, 0};
|
|
return val & kExtractMasks[tag_type];
|
|
#endif
|
|
};
|
|
|
|
// Core decompression loop, when there is enough data available.
|
|
// Decompresses the input buffer [ip, ip_limit) into the output buffer
|
|
// [op, op_limit_min_slop). Returning when either we are too close to the end
|
|
// of the input buffer, or we exceed op_limit_min_slop or when a exceptional
|
|
// tag is encountered (literal of length > 60) or a copy-4.
|
|
// Returns {ip, op} at the points it stopped decoding.
|
|
// TODO This function probably does not need to be inlined, as it
|
|
// should decode large chunks at a time. This allows runtime dispatch to
|
|
// implementations based on CPU capability (BMI2 / perhaps 32 / 64 byte memcpy).
|
|
template <typename T>
|
|
std::pair<const uint8_t*, ptrdiff_t> DecompressBranchless(
|
|
const uint8_t* ip, const uint8_t* ip_limit, ptrdiff_t op, T op_base,
|
|
ptrdiff_t op_limit_min_slop) {
|
|
// We unroll the inner loop twice so we need twice the spare room.
|
|
op_limit_min_slop -= kSlopBytes;
|
|
if (2 * (kSlopBytes + 1) < ip_limit - ip && op < op_limit_min_slop) {
|
|
const uint8_t* const ip_limit_min_slop = ip_limit - 2 * kSlopBytes - 1;
|
|
ip++;
|
|
// ip points just past the tag and we are touching at maximum kSlopBytes
|
|
// in an iteration.
|
|
size_t tag = ip[-1];
|
|
#if defined(__clang__) && defined(__aarch64__)
|
|
// Workaround for https://bugs.llvm.org/show_bug.cgi?id=51317
|
|
// when loading 1 byte, clang for aarch64 doesn't realize that it(ldrb)
|
|
// comes with free zero-extension, so clang generates another
|
|
// 'and xn, xm, 0xff' before it use that as the offset. This 'and' is
|
|
// redundant and can be removed by adding this dummy asm, which gives
|
|
// clang a hint that we're doing the zero-extension at the load.
|
|
asm("" ::"r"(tag));
|
|
#endif
|
|
do {
|
|
// The throughput is limited by instructions, unrolling the inner loop
|
|
// twice reduces the amount of instructions checking limits and also
|
|
// leads to reduced mov's.
|
|
for (int i = 0; i < 2; i++) {
|
|
const uint8_t* old_ip = ip;
|
|
assert(tag == ip[-1]);
|
|
// For literals tag_type = 0, hence we will always obtain 0 from
|
|
// ExtractLowBytes. For literals offset will thus be kLiteralOffset.
|
|
ptrdiff_t len_min_offset = kLengthMinusOffset[tag];
|
|
#if defined(__aarch64__)
|
|
size_t tag_type = AdvanceToNextTagARMOptimized(&ip, &tag);
|
|
#else
|
|
size_t tag_type = AdvanceToNextTagX86Optimized(&ip, &tag);
|
|
#endif
|
|
uint32_t next = LittleEndian::Load32(old_ip);
|
|
size_t len = len_min_offset & 0xFF;
|
|
len_min_offset -= ExtractOffset(next, tag_type);
|
|
if (SNAPPY_PREDICT_FALSE(len_min_offset > 0)) {
|
|
if (SNAPPY_PREDICT_FALSE(len & 0x80)) {
|
|
// Exceptional case (long literal or copy 4).
|
|
// Actually doing the copy here is negatively impacting the main
|
|
// loop due to compiler incorrectly allocating a register for
|
|
// this fallback. Hence we just break.
|
|
break_loop:
|
|
ip = old_ip;
|
|
goto exit;
|
|
}
|
|
// Only copy-1 or copy-2 tags can get here.
|
|
assert(tag_type == 1 || tag_type == 2);
|
|
std::ptrdiff_t delta = op + len_min_offset - len;
|
|
// Guard against copies before the buffer start.
|
|
if (SNAPPY_PREDICT_FALSE(delta < 0 ||
|
|
!Copy64BytesWithPatternExtension(
|
|
op_base + op, len - len_min_offset))) {
|
|
goto break_loop;
|
|
}
|
|
op += len;
|
|
continue;
|
|
}
|
|
std::ptrdiff_t delta = op + len_min_offset - len;
|
|
if (SNAPPY_PREDICT_FALSE(delta < 0)) {
|
|
// Due to the spurious offset in literals have this will trigger
|
|
// at the start of a block when op is still smaller than 256.
|
|
if (tag_type != 0) goto break_loop;
|
|
MemCopy64(op_base + op, old_ip, len);
|
|
op += len;
|
|
continue;
|
|
}
|
|
|
|
// For copies we need to copy from op_base + delta, for literals
|
|
// we need to copy from ip instead of from the stream.
|
|
const void* from =
|
|
tag_type ? reinterpret_cast<void*>(op_base + delta) : old_ip;
|
|
MemCopy64(op_base + op, from, len);
|
|
op += len;
|
|
}
|
|
} while (ip < ip_limit_min_slop && op < op_limit_min_slop);
|
|
exit:
|
|
ip--;
|
|
assert(ip <= ip_limit);
|
|
}
|
|
return {ip, op};
|
|
}
|
|
|
|
// Helper class for decompression
|
|
class SnappyDecompressor {
|
|
private:
|
|
Source* reader_; // Underlying source of bytes to decompress
|
|
const char* ip_; // Points to next buffered byte
|
|
const char* ip_limit_; // Points just past buffered bytes
|
|
// If ip < ip_limit_min_maxtaglen_ it's safe to read kMaxTagLength from
|
|
// buffer.
|
|
const char* ip_limit_min_maxtaglen_;
|
|
uint32_t peeked_; // Bytes peeked from reader (need to skip)
|
|
bool eof_; // Hit end of input without an error?
|
|
char scratch_[kMaximumTagLength]; // See RefillTag().
|
|
|
|
// Ensure that all of the tag metadata for the next tag is available
|
|
// in [ip_..ip_limit_-1]. Also ensures that [ip,ip+4] is readable even
|
|
// if (ip_limit_ - ip_ < 5).
|
|
//
|
|
// Returns true on success, false on error or end of input.
|
|
bool RefillTag();
|
|
|
|
void ResetLimit(const char* ip) {
|
|
ip_limit_min_maxtaglen_ =
|
|
ip_limit_ - std::min<ptrdiff_t>(ip_limit_ - ip, kMaximumTagLength - 1);
|
|
}
|
|
|
|
public:
|
|
explicit SnappyDecompressor(Source* reader)
|
|
: reader_(reader), ip_(NULL), ip_limit_(NULL), peeked_(0), eof_(false) {}
|
|
|
|
~SnappyDecompressor() {
|
|
// Advance past any bytes we peeked at from the reader
|
|
reader_->Skip(peeked_);
|
|
}
|
|
|
|
// Returns true iff we have hit the end of the input without an error.
|
|
bool eof() const { return eof_; }
|
|
|
|
// Read the uncompressed length stored at the start of the compressed data.
|
|
// On success, stores the length in *result and returns true.
|
|
// On failure, returns false.
|
|
bool ReadUncompressedLength(uint32_t* result) {
|
|
assert(ip_ == NULL); // Must not have read anything yet
|
|
// Length is encoded in 1..5 bytes
|
|
*result = 0;
|
|
uint32_t shift = 0;
|
|
while (true) {
|
|
if (shift >= 32) return false;
|
|
size_t n;
|
|
const char* ip = reader_->Peek(&n);
|
|
if (n == 0) return false;
|
|
const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
|
|
reader_->Skip(1);
|
|
uint32_t val = c & 0x7f;
|
|
if (LeftShiftOverflows(static_cast<uint8_t>(val), shift)) return false;
|
|
*result |= val << shift;
|
|
if (c < 128) {
|
|
break;
|
|
}
|
|
shift += 7;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
// Process the next item found in the input.
|
|
// Returns true if successful, false on error or end of input.
|
|
template <class Writer>
|
|
#if defined(__GNUC__) && defined(__x86_64__)
|
|
__attribute__((aligned(32)))
|
|
#endif
|
|
void
|
|
DecompressAllTags(Writer* writer) {
|
|
const char* ip = ip_;
|
|
ResetLimit(ip);
|
|
auto op = writer->GetOutputPtr();
|
|
// We could have put this refill fragment only at the beginning of the loop.
|
|
// However, duplicating it at the end of each branch gives the compiler more
|
|
// scope to optimize the <ip_limit_ - ip> expression based on the local
|
|
// context, which overall increases speed.
|
|
#define MAYBE_REFILL() \
|
|
if (SNAPPY_PREDICT_FALSE(ip >= ip_limit_min_maxtaglen_)) { \
|
|
ip_ = ip; \
|
|
if (SNAPPY_PREDICT_FALSE(!RefillTag())) goto exit; \
|
|
ip = ip_; \
|
|
ResetLimit(ip); \
|
|
} \
|
|
preload = static_cast<uint8_t>(*ip)
|
|
|
|
// At the start of the for loop below the least significant byte of preload
|
|
// contains the tag.
|
|
uint32_t preload;
|
|
MAYBE_REFILL();
|
|
for (;;) {
|
|
{
|
|
ptrdiff_t op_limit_min_slop;
|
|
auto op_base = writer->GetBase(&op_limit_min_slop);
|
|
if (op_base) {
|
|
auto res =
|
|
DecompressBranchless(reinterpret_cast<const uint8_t*>(ip),
|
|
reinterpret_cast<const uint8_t*>(ip_limit_),
|
|
op - op_base, op_base, op_limit_min_slop);
|
|
ip = reinterpret_cast<const char*>(res.first);
|
|
op = op_base + res.second;
|
|
MAYBE_REFILL();
|
|
}
|
|
}
|
|
const uint8_t c = static_cast<uint8_t>(preload);
|
|
ip++;
|
|
|
|
// Ratio of iterations that have LITERAL vs non-LITERAL for different
|
|
// inputs.
|
|
//
|
|
// input LITERAL NON_LITERAL
|
|
// -----------------------------------
|
|
// html|html4|cp 23% 77%
|
|
// urls 36% 64%
|
|
// jpg 47% 53%
|
|
// pdf 19% 81%
|
|
// txt[1-4] 25% 75%
|
|
// pb 24% 76%
|
|
// bin 24% 76%
|
|
if (SNAPPY_PREDICT_FALSE((c & 0x3) == LITERAL)) {
|
|
size_t literal_length = (c >> 2) + 1u;
|
|
if (writer->TryFastAppend(ip, ip_limit_ - ip, literal_length, &op)) {
|
|
assert(literal_length < 61);
|
|
ip += literal_length;
|
|
// NOTE: There is no MAYBE_REFILL() here, as TryFastAppend()
|
|
// will not return true unless there's already at least five spare
|
|
// bytes in addition to the literal.
|
|
preload = static_cast<uint8_t>(*ip);
|
|
continue;
|
|
}
|
|
if (SNAPPY_PREDICT_FALSE(literal_length >= 61)) {
|
|
// Long literal.
|
|
const size_t literal_length_length = literal_length - 60;
|
|
literal_length =
|
|
ExtractLowBytes(LittleEndian::Load32(ip), literal_length_length) +
|
|
1;
|
|
ip += literal_length_length;
|
|
}
|
|
|
|
size_t avail = ip_limit_ - ip;
|
|
while (avail < literal_length) {
|
|
if (!writer->Append(ip, avail, &op)) goto exit;
|
|
literal_length -= avail;
|
|
reader_->Skip(peeked_);
|
|
size_t n;
|
|
ip = reader_->Peek(&n);
|
|
avail = n;
|
|
peeked_ = avail;
|
|
if (avail == 0) goto exit;
|
|
ip_limit_ = ip + avail;
|
|
ResetLimit(ip);
|
|
}
|
|
if (!writer->Append(ip, literal_length, &op)) goto exit;
|
|
ip += literal_length;
|
|
MAYBE_REFILL();
|
|
} else {
|
|
if (SNAPPY_PREDICT_FALSE((c & 3) == COPY_4_BYTE_OFFSET)) {
|
|
const size_t copy_offset = LittleEndian::Load32(ip);
|
|
const size_t length = (c >> 2) + 1;
|
|
ip += 4;
|
|
|
|
if (!writer->AppendFromSelf(copy_offset, length, &op)) goto exit;
|
|
} else {
|
|
const ptrdiff_t entry = kLengthMinusOffset[c];
|
|
preload = LittleEndian::Load32(ip);
|
|
const uint32_t trailer = ExtractLowBytes(preload, c & 3);
|
|
const uint32_t length = entry & 0xff;
|
|
assert(length > 0);
|
|
|
|
// copy_offset/256 is encoded in bits 8..10. By just fetching
|
|
// those bits, we get copy_offset (since the bit-field starts at
|
|
// bit 8).
|
|
const uint32_t copy_offset = trailer - entry + length;
|
|
if (!writer->AppendFromSelf(copy_offset, length, &op)) goto exit;
|
|
|
|
ip += (c & 3);
|
|
// By using the result of the previous load we reduce the critical
|
|
// dependency chain of ip to 4 cycles.
|
|
preload >>= (c & 3) * 8;
|
|
if (ip < ip_limit_min_maxtaglen_) continue;
|
|
}
|
|
MAYBE_REFILL();
|
|
}
|
|
}
|
|
#undef MAYBE_REFILL
|
|
exit:
|
|
writer->SetOutputPtr(op);
|
|
}
|
|
};
|
|
|
|
constexpr uint32_t CalculateNeeded(uint8_t tag) {
|
|
return ((tag & 3) == 0 && tag >= (60 * 4))
|
|
? (tag >> 2) - 58
|
|
: (0x05030201 >> ((tag * 8) & 31)) & 0xFF;
|
|
}
|
|
|
|
#if __cplusplus >= 201402L
|
|
constexpr bool VerifyCalculateNeeded() {
|
|
for (int i = 0; i < 1; i++) {
|
|
if (CalculateNeeded(i) != (char_table[i] >> 11) + 1) return false;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
// Make sure CalculateNeeded is correct by verifying it against the established
|
|
// table encoding the number of added bytes needed.
|
|
static_assert(VerifyCalculateNeeded(), "");
|
|
#endif // c++14
|
|
|
|
bool SnappyDecompressor::RefillTag() {
|
|
const char* ip = ip_;
|
|
if (ip == ip_limit_) {
|
|
// Fetch a new fragment from the reader
|
|
reader_->Skip(peeked_); // All peeked bytes are used up
|
|
size_t n;
|
|
ip = reader_->Peek(&n);
|
|
peeked_ = n;
|
|
eof_ = (n == 0);
|
|
if (eof_) return false;
|
|
ip_limit_ = ip + n;
|
|
}
|
|
|
|
// Read the tag character
|
|
assert(ip < ip_limit_);
|
|
const unsigned char c = *(reinterpret_cast<const unsigned char*>(ip));
|
|
// At this point make sure that the data for the next tag is consecutive.
|
|
// For copy 1 this means the next 2 bytes (tag and 1 byte offset)
|
|
// For copy 2 the next 3 bytes (tag and 2 byte offset)
|
|
// For copy 4 the next 5 bytes (tag and 4 byte offset)
|
|
// For all small literals we only need 1 byte buf for literals 60...63 the
|
|
// length is encoded in 1...4 extra bytes.
|
|
const uint32_t needed = CalculateNeeded(c);
|
|
assert(needed <= sizeof(scratch_));
|
|
|
|
// Read more bytes from reader if needed
|
|
uint32_t nbuf = ip_limit_ - ip;
|
|
if (nbuf < needed) {
|
|
// Stitch together bytes from ip and reader to form the word
|
|
// contents. We store the needed bytes in "scratch_". They
|
|
// will be consumed immediately by the caller since we do not
|
|
// read more than we need.
|
|
std::memmove(scratch_, ip, nbuf);
|
|
reader_->Skip(peeked_); // All peeked bytes are used up
|
|
peeked_ = 0;
|
|
while (nbuf < needed) {
|
|
size_t length;
|
|
const char* src = reader_->Peek(&length);
|
|
if (length == 0) return false;
|
|
uint32_t to_add = std::min<uint32_t>(needed - nbuf, length);
|
|
std::memcpy(scratch_ + nbuf, src, to_add);
|
|
nbuf += to_add;
|
|
reader_->Skip(to_add);
|
|
}
|
|
assert(nbuf == needed);
|
|
ip_ = scratch_;
|
|
ip_limit_ = scratch_ + needed;
|
|
} else if (nbuf < kMaximumTagLength) {
|
|
// Have enough bytes, but move into scratch_ so that we do not
|
|
// read past end of input
|
|
std::memmove(scratch_, ip, nbuf);
|
|
reader_->Skip(peeked_); // All peeked bytes are used up
|
|
peeked_ = 0;
|
|
ip_ = scratch_;
|
|
ip_limit_ = scratch_ + nbuf;
|
|
} else {
|
|
// Pass pointer to buffer returned by reader_.
|
|
ip_ = ip;
|
|
}
|
|
return true;
|
|
}
|
|
|
|
template <typename Writer>
|
|
static bool InternalUncompress(Source* r, Writer* writer) {
|
|
// Read the uncompressed length from the front of the compressed input
|
|
SnappyDecompressor decompressor(r);
|
|
uint32_t uncompressed_len = 0;
|
|
if (!decompressor.ReadUncompressedLength(&uncompressed_len)) return false;
|
|
|
|
return InternalUncompressAllTags(&decompressor, writer, r->Available(),
|
|
uncompressed_len);
|
|
}
|
|
|
|
template <typename Writer>
|
|
static bool InternalUncompressAllTags(SnappyDecompressor* decompressor,
|
|
Writer* writer, uint32_t compressed_len,
|
|
uint32_t uncompressed_len) {
|
|
Report("snappy_uncompress", compressed_len, uncompressed_len);
|
|
|
|
writer->SetExpectedLength(uncompressed_len);
|
|
|
|
// Process the entire input
|
|
decompressor->DecompressAllTags(writer);
|
|
writer->Flush();
|
|
return (decompressor->eof() && writer->CheckLength());
|
|
}
|
|
|
|
bool GetUncompressedLength(Source* source, uint32_t* result) {
|
|
SnappyDecompressor decompressor(source);
|
|
return decompressor.ReadUncompressedLength(result);
|
|
}
|
|
|
|
size_t Compress(Source* reader, Sink* writer) {
|
|
size_t written = 0;
|
|
size_t N = reader->Available();
|
|
const size_t uncompressed_size = N;
|
|
char ulength[Varint::kMax32];
|
|
char* p = Varint::Encode32(ulength, N);
|
|
writer->Append(ulength, p - ulength);
|
|
written += (p - ulength);
|
|
|
|
internal::WorkingMemory wmem(N);
|
|
|
|
while (N > 0) {
|
|
// Get next block to compress (without copying if possible)
|
|
size_t fragment_size;
|
|
const char* fragment = reader->Peek(&fragment_size);
|
|
assert(fragment_size != 0); // premature end of input
|
|
const size_t num_to_read = std::min(N, kBlockSize);
|
|
size_t bytes_read = fragment_size;
|
|
|
|
size_t pending_advance = 0;
|
|
if (bytes_read >= num_to_read) {
|
|
// Buffer returned by reader is large enough
|
|
pending_advance = num_to_read;
|
|
fragment_size = num_to_read;
|
|
} else {
|
|
char* scratch = wmem.GetScratchInput();
|
|
std::memcpy(scratch, fragment, bytes_read);
|
|
reader->Skip(bytes_read);
|
|
|
|
while (bytes_read < num_to_read) {
|
|
fragment = reader->Peek(&fragment_size);
|
|
size_t n = std::min<size_t>(fragment_size, num_to_read - bytes_read);
|
|
std::memcpy(scratch + bytes_read, fragment, n);
|
|
bytes_read += n;
|
|
reader->Skip(n);
|
|
}
|
|
assert(bytes_read == num_to_read);
|
|
fragment = scratch;
|
|
fragment_size = num_to_read;
|
|
}
|
|
assert(fragment_size == num_to_read);
|
|
|
|
// Get encoding table for compression
|
|
int table_size;
|
|
uint16_t* table = wmem.GetHashTable(num_to_read, &table_size);
|
|
|
|
// Compress input_fragment and append to dest
|
|
const int max_output = MaxCompressedLength(num_to_read);
|
|
|
|
// Need a scratch buffer for the output, in case the byte sink doesn't
|
|
// have room for us directly.
|
|
|
|
// Since we encode kBlockSize regions followed by a region
|
|
// which is <= kBlockSize in length, a previously allocated
|
|
// scratch_output[] region is big enough for this iteration.
|
|
char* dest = writer->GetAppendBuffer(max_output, wmem.GetScratchOutput());
|
|
char* end = internal::CompressFragment(fragment, fragment_size, dest, table,
|
|
table_size);
|
|
writer->Append(dest, end - dest);
|
|
written += (end - dest);
|
|
|
|
N -= num_to_read;
|
|
reader->Skip(pending_advance);
|
|
}
|
|
|
|
Report("snappy_compress", written, uncompressed_size);
|
|
|
|
return written;
|
|
}
|
|
|
|
// -----------------------------------------------------------------------
|
|
// IOVec interfaces
|
|
// -----------------------------------------------------------------------
|
|
|
|
// A `Source` implementation that yields the contents of an `iovec` array. Note
|
|
// that `total_size` is the total number of bytes to be read from the elements
|
|
// of `iov` (_not_ the total number of elements in `iov`).
|
|
class SnappyIOVecReader : public Source {
|
|
public:
|
|
SnappyIOVecReader(const struct iovec* iov, size_t total_size)
|
|
: curr_iov_(iov),
|
|
curr_pos_(total_size > 0 ? reinterpret_cast<const char*>(iov->iov_base)
|
|
: nullptr),
|
|
curr_size_remaining_(total_size > 0 ? iov->iov_len : 0),
|
|
total_size_remaining_(total_size) {
|
|
// Skip empty leading `iovec`s.
|
|
if (total_size > 0 && curr_size_remaining_ == 0) Advance();
|
|
}
|
|
|
|
~SnappyIOVecReader() = default;
|
|
|
|
size_t Available() const { return total_size_remaining_; }
|
|
|
|
const char* Peek(size_t* len) {
|
|
*len = curr_size_remaining_;
|
|
return curr_pos_;
|
|
}
|
|
|
|
void Skip(size_t n) {
|
|
while (n >= curr_size_remaining_ && n > 0) {
|
|
n -= curr_size_remaining_;
|
|
Advance();
|
|
}
|
|
curr_size_remaining_ -= n;
|
|
total_size_remaining_ -= n;
|
|
curr_pos_ += n;
|
|
}
|
|
|
|
private:
|
|
// Advances to the next nonempty `iovec` and updates related variables.
|
|
void Advance() {
|
|
do {
|
|
assert(total_size_remaining_ >= curr_size_remaining_);
|
|
total_size_remaining_ -= curr_size_remaining_;
|
|
if (total_size_remaining_ == 0) {
|
|
curr_pos_ = nullptr;
|
|
curr_size_remaining_ = 0;
|
|
return;
|
|
}
|
|
++curr_iov_;
|
|
curr_pos_ = reinterpret_cast<const char*>(curr_iov_->iov_base);
|
|
curr_size_remaining_ = curr_iov_->iov_len;
|
|
} while (curr_size_remaining_ == 0);
|
|
}
|
|
|
|
// The `iovec` currently being read.
|
|
const struct iovec* curr_iov_;
|
|
// The location in `curr_iov_` currently being read.
|
|
const char* curr_pos_;
|
|
// The amount of unread data in `curr_iov_`.
|
|
size_t curr_size_remaining_;
|
|
// The amount of unread data in the entire input array.
|
|
size_t total_size_remaining_;
|
|
};
|
|
|
|
// A type that writes to an iovec.
|
|
// Note that this is not a "ByteSink", but a type that matches the
|
|
// Writer template argument to SnappyDecompressor::DecompressAllTags().
|
|
class SnappyIOVecWriter {
|
|
private:
|
|
// output_iov_end_ is set to iov + count and used to determine when
|
|
// the end of the iovs is reached.
|
|
const struct iovec* output_iov_end_;
|
|
|
|
#if !defined(NDEBUG)
|
|
const struct iovec* output_iov_;
|
|
#endif // !defined(NDEBUG)
|
|
|
|
// Current iov that is being written into.
|
|
const struct iovec* curr_iov_;
|
|
|
|
// Pointer to current iov's write location.
|
|
char* curr_iov_output_;
|
|
|
|
// Remaining bytes to write into curr_iov_output.
|
|
size_t curr_iov_remaining_;
|
|
|
|
// Total bytes decompressed into output_iov_ so far.
|
|
size_t total_written_;
|
|
|
|
// Maximum number of bytes that will be decompressed into output_iov_.
|
|
size_t output_limit_;
|
|
|
|
static inline char* GetIOVecPointer(const struct iovec* iov, size_t offset) {
|
|
return reinterpret_cast<char*>(iov->iov_base) + offset;
|
|
}
|
|
|
|
public:
|
|
// Does not take ownership of iov. iov must be valid during the
|
|
// entire lifetime of the SnappyIOVecWriter.
|
|
inline SnappyIOVecWriter(const struct iovec* iov, size_t iov_count)
|
|
: output_iov_end_(iov + iov_count),
|
|
#if !defined(NDEBUG)
|
|
output_iov_(iov),
|
|
#endif // !defined(NDEBUG)
|
|
curr_iov_(iov),
|
|
curr_iov_output_(iov_count ? reinterpret_cast<char*>(iov->iov_base)
|
|
: nullptr),
|
|
curr_iov_remaining_(iov_count ? iov->iov_len : 0),
|
|
total_written_(0),
|
|
output_limit_(-1) {
|
|
}
|
|
|
|
inline void SetExpectedLength(size_t len) { output_limit_ = len; }
|
|
|
|
inline bool CheckLength() const { return total_written_ == output_limit_; }
|
|
|
|
inline bool Append(const char* ip, size_t len, char**) {
|
|
if (total_written_ + len > output_limit_) {
|
|
return false;
|
|
}
|
|
|
|
return AppendNoCheck(ip, len);
|
|
}
|
|
|
|
char* GetOutputPtr() { return nullptr; }
|
|
char* GetBase(ptrdiff_t*) { return nullptr; }
|
|
void SetOutputPtr(char* op) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)op;
|
|
}
|
|
|
|
inline bool AppendNoCheck(const char* ip, size_t len) {
|
|
while (len > 0) {
|
|
if (curr_iov_remaining_ == 0) {
|
|
// This iovec is full. Go to the next one.
|
|
if (curr_iov_ + 1 >= output_iov_end_) {
|
|
return false;
|
|
}
|
|
++curr_iov_;
|
|
curr_iov_output_ = reinterpret_cast<char*>(curr_iov_->iov_base);
|
|
curr_iov_remaining_ = curr_iov_->iov_len;
|
|
}
|
|
|
|
const size_t to_write = std::min(len, curr_iov_remaining_);
|
|
std::memcpy(curr_iov_output_, ip, to_write);
|
|
curr_iov_output_ += to_write;
|
|
curr_iov_remaining_ -= to_write;
|
|
total_written_ += to_write;
|
|
ip += to_write;
|
|
len -= to_write;
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
inline bool TryFastAppend(const char* ip, size_t available, size_t len,
|
|
char**) {
|
|
const size_t space_left = output_limit_ - total_written_;
|
|
if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16 &&
|
|
curr_iov_remaining_ >= 16) {
|
|
// Fast path, used for the majority (about 95%) of invocations.
|
|
UnalignedCopy128(ip, curr_iov_output_);
|
|
curr_iov_output_ += len;
|
|
curr_iov_remaining_ -= len;
|
|
total_written_ += len;
|
|
return true;
|
|
}
|
|
|
|
return false;
|
|
}
|
|
|
|
inline bool AppendFromSelf(size_t offset, size_t len, char**) {
|
|
// See SnappyArrayWriter::AppendFromSelf for an explanation of
|
|
// the "offset - 1u" trick.
|
|
if (offset - 1u >= total_written_) {
|
|
return false;
|
|
}
|
|
const size_t space_left = output_limit_ - total_written_;
|
|
if (len > space_left) {
|
|
return false;
|
|
}
|
|
|
|
// Locate the iovec from which we need to start the copy.
|
|
const iovec* from_iov = curr_iov_;
|
|
size_t from_iov_offset = curr_iov_->iov_len - curr_iov_remaining_;
|
|
while (offset > 0) {
|
|
if (from_iov_offset >= offset) {
|
|
from_iov_offset -= offset;
|
|
break;
|
|
}
|
|
|
|
offset -= from_iov_offset;
|
|
--from_iov;
|
|
#if !defined(NDEBUG)
|
|
assert(from_iov >= output_iov_);
|
|
#endif // !defined(NDEBUG)
|
|
from_iov_offset = from_iov->iov_len;
|
|
}
|
|
|
|
// Copy <len> bytes starting from the iovec pointed to by from_iov_index to
|
|
// the current iovec.
|
|
while (len > 0) {
|
|
assert(from_iov <= curr_iov_);
|
|
if (from_iov != curr_iov_) {
|
|
const size_t to_copy =
|
|
std::min(from_iov->iov_len - from_iov_offset, len);
|
|
AppendNoCheck(GetIOVecPointer(from_iov, from_iov_offset), to_copy);
|
|
len -= to_copy;
|
|
if (len > 0) {
|
|
++from_iov;
|
|
from_iov_offset = 0;
|
|
}
|
|
} else {
|
|
size_t to_copy = curr_iov_remaining_;
|
|
if (to_copy == 0) {
|
|
// This iovec is full. Go to the next one.
|
|
if (curr_iov_ + 1 >= output_iov_end_) {
|
|
return false;
|
|
}
|
|
++curr_iov_;
|
|
curr_iov_output_ = reinterpret_cast<char*>(curr_iov_->iov_base);
|
|
curr_iov_remaining_ = curr_iov_->iov_len;
|
|
continue;
|
|
}
|
|
if (to_copy > len) {
|
|
to_copy = len;
|
|
}
|
|
assert(to_copy > 0);
|
|
|
|
IncrementalCopy(GetIOVecPointer(from_iov, from_iov_offset),
|
|
curr_iov_output_, curr_iov_output_ + to_copy,
|
|
curr_iov_output_ + curr_iov_remaining_);
|
|
curr_iov_output_ += to_copy;
|
|
curr_iov_remaining_ -= to_copy;
|
|
from_iov_offset += to_copy;
|
|
total_written_ += to_copy;
|
|
len -= to_copy;
|
|
}
|
|
}
|
|
|
|
return true;
|
|
}
|
|
|
|
inline void Flush() {}
|
|
};
|
|
|
|
bool RawUncompressToIOVec(const char* compressed, size_t compressed_length,
|
|
const struct iovec* iov, size_t iov_cnt) {
|
|
ByteArraySource reader(compressed, compressed_length);
|
|
return RawUncompressToIOVec(&reader, iov, iov_cnt);
|
|
}
|
|
|
|
bool RawUncompressToIOVec(Source* compressed, const struct iovec* iov,
|
|
size_t iov_cnt) {
|
|
SnappyIOVecWriter output(iov, iov_cnt);
|
|
return InternalUncompress(compressed, &output);
|
|
}
|
|
|
|
// -----------------------------------------------------------------------
|
|
// Flat array interfaces
|
|
// -----------------------------------------------------------------------
|
|
|
|
// A type that writes to a flat array.
|
|
// Note that this is not a "ByteSink", but a type that matches the
|
|
// Writer template argument to SnappyDecompressor::DecompressAllTags().
|
|
class SnappyArrayWriter {
|
|
private:
|
|
char* base_;
|
|
char* op_;
|
|
char* op_limit_;
|
|
// If op < op_limit_min_slop_ then it's safe to unconditionally write
|
|
// kSlopBytes starting at op.
|
|
char* op_limit_min_slop_;
|
|
|
|
public:
|
|
inline explicit SnappyArrayWriter(char* dst)
|
|
: base_(dst),
|
|
op_(dst),
|
|
op_limit_(dst),
|
|
op_limit_min_slop_(dst) {} // Safe default see invariant.
|
|
|
|
inline void SetExpectedLength(size_t len) {
|
|
op_limit_ = op_ + len;
|
|
// Prevent pointer from being past the buffer.
|
|
op_limit_min_slop_ = op_limit_ - std::min<size_t>(kSlopBytes - 1, len);
|
|
}
|
|
|
|
inline bool CheckLength() const { return op_ == op_limit_; }
|
|
|
|
char* GetOutputPtr() { return op_; }
|
|
char* GetBase(ptrdiff_t* op_limit_min_slop) {
|
|
*op_limit_min_slop = op_limit_min_slop_ - base_;
|
|
return base_;
|
|
}
|
|
void SetOutputPtr(char* op) { op_ = op; }
|
|
|
|
inline bool Append(const char* ip, size_t len, char** op_p) {
|
|
char* op = *op_p;
|
|
const size_t space_left = op_limit_ - op;
|
|
if (space_left < len) return false;
|
|
std::memcpy(op, ip, len);
|
|
*op_p = op + len;
|
|
return true;
|
|
}
|
|
|
|
inline bool TryFastAppend(const char* ip, size_t available, size_t len,
|
|
char** op_p) {
|
|
char* op = *op_p;
|
|
const size_t space_left = op_limit_ - op;
|
|
if (len <= 16 && available >= 16 + kMaximumTagLength && space_left >= 16) {
|
|
// Fast path, used for the majority (about 95%) of invocations.
|
|
UnalignedCopy128(ip, op);
|
|
*op_p = op + len;
|
|
return true;
|
|
} else {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
SNAPPY_ATTRIBUTE_ALWAYS_INLINE
|
|
inline bool AppendFromSelf(size_t offset, size_t len, char** op_p) {
|
|
assert(len > 0);
|
|
char* const op = *op_p;
|
|
assert(op >= base_);
|
|
char* const op_end = op + len;
|
|
|
|
// Check if we try to append from before the start of the buffer.
|
|
if (SNAPPY_PREDICT_FALSE(static_cast<size_t>(op - base_) < offset))
|
|
return false;
|
|
|
|
if (SNAPPY_PREDICT_FALSE((kSlopBytes < 64 && len > kSlopBytes) ||
|
|
op >= op_limit_min_slop_ || offset < len)) {
|
|
if (op_end > op_limit_ || offset == 0) return false;
|
|
*op_p = IncrementalCopy(op - offset, op, op_end, op_limit_);
|
|
return true;
|
|
}
|
|
std::memmove(op, op - offset, kSlopBytes);
|
|
*op_p = op_end;
|
|
return true;
|
|
}
|
|
inline size_t Produced() const {
|
|
assert(op_ >= base_);
|
|
return op_ - base_;
|
|
}
|
|
inline void Flush() {}
|
|
};
|
|
|
|
bool RawUncompress(const char* compressed, size_t compressed_length,
|
|
char* uncompressed) {
|
|
ByteArraySource reader(compressed, compressed_length);
|
|
return RawUncompress(&reader, uncompressed);
|
|
}
|
|
|
|
bool RawUncompress(Source* compressed, char* uncompressed) {
|
|
SnappyArrayWriter output(uncompressed);
|
|
return InternalUncompress(compressed, &output);
|
|
}
|
|
|
|
bool Uncompress(const char* compressed, size_t compressed_length,
|
|
std::string* uncompressed) {
|
|
size_t ulength;
|
|
if (!GetUncompressedLength(compressed, compressed_length, &ulength)) {
|
|
return false;
|
|
}
|
|
// On 32-bit builds: max_size() < kuint32max. Check for that instead
|
|
// of crashing (e.g., consider externally specified compressed data).
|
|
if (ulength > uncompressed->max_size()) {
|
|
return false;
|
|
}
|
|
STLStringResizeUninitialized(uncompressed, ulength);
|
|
return RawUncompress(compressed, compressed_length,
|
|
string_as_array(uncompressed));
|
|
}
|
|
|
|
// A Writer that drops everything on the floor and just does validation
|
|
class SnappyDecompressionValidator {
|
|
private:
|
|
size_t expected_;
|
|
size_t produced_;
|
|
|
|
public:
|
|
inline SnappyDecompressionValidator() : expected_(0), produced_(0) {}
|
|
inline void SetExpectedLength(size_t len) { expected_ = len; }
|
|
size_t GetOutputPtr() { return produced_; }
|
|
size_t GetBase(ptrdiff_t* op_limit_min_slop) {
|
|
*op_limit_min_slop = std::numeric_limits<ptrdiff_t>::max() - kSlopBytes + 1;
|
|
return 1;
|
|
}
|
|
void SetOutputPtr(size_t op) { produced_ = op; }
|
|
inline bool CheckLength() const { return expected_ == produced_; }
|
|
inline bool Append(const char* ip, size_t len, size_t* produced) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)ip;
|
|
|
|
*produced += len;
|
|
return *produced <= expected_;
|
|
}
|
|
inline bool TryFastAppend(const char* ip, size_t available, size_t length,
|
|
size_t* produced) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)ip;
|
|
(void)available;
|
|
(void)length;
|
|
(void)produced;
|
|
|
|
return false;
|
|
}
|
|
inline bool AppendFromSelf(size_t offset, size_t len, size_t* produced) {
|
|
// See SnappyArrayWriter::AppendFromSelf for an explanation of
|
|
// the "offset - 1u" trick.
|
|
if (*produced <= offset - 1u) return false;
|
|
*produced += len;
|
|
return *produced <= expected_;
|
|
}
|
|
inline void Flush() {}
|
|
};
|
|
|
|
bool IsValidCompressedBuffer(const char* compressed, size_t compressed_length) {
|
|
ByteArraySource reader(compressed, compressed_length);
|
|
SnappyDecompressionValidator writer;
|
|
return InternalUncompress(&reader, &writer);
|
|
}
|
|
|
|
bool IsValidCompressed(Source* compressed) {
|
|
SnappyDecompressionValidator writer;
|
|
return InternalUncompress(compressed, &writer);
|
|
}
|
|
|
|
void RawCompress(const char* input, size_t input_length, char* compressed,
|
|
size_t* compressed_length) {
|
|
ByteArraySource reader(input, input_length);
|
|
UncheckedByteArraySink writer(compressed);
|
|
Compress(&reader, &writer);
|
|
|
|
// Compute how many bytes were added
|
|
*compressed_length = (writer.CurrentDestination() - compressed);
|
|
}
|
|
|
|
void RawCompressFromIOVec(const struct iovec* iov, size_t uncompressed_length,
|
|
char* compressed, size_t* compressed_length) {
|
|
SnappyIOVecReader reader(iov, uncompressed_length);
|
|
UncheckedByteArraySink writer(compressed);
|
|
Compress(&reader, &writer);
|
|
|
|
// Compute how many bytes were added.
|
|
*compressed_length = writer.CurrentDestination() - compressed;
|
|
}
|
|
|
|
size_t Compress(const char* input, size_t input_length,
|
|
std::string* compressed) {
|
|
// Pre-grow the buffer to the max length of the compressed output
|
|
STLStringResizeUninitialized(compressed, MaxCompressedLength(input_length));
|
|
|
|
size_t compressed_length;
|
|
RawCompress(input, input_length, string_as_array(compressed),
|
|
&compressed_length);
|
|
compressed->erase(compressed_length);
|
|
return compressed_length;
|
|
}
|
|
|
|
size_t CompressFromIOVec(const struct iovec* iov, size_t iov_cnt,
|
|
std::string* compressed) {
|
|
// Compute the number of bytes to be compressed.
|
|
size_t uncompressed_length = 0;
|
|
for (int i = 0; i < iov_cnt; ++i) {
|
|
uncompressed_length += iov[i].iov_len;
|
|
}
|
|
|
|
// Pre-grow the buffer to the max length of the compressed output.
|
|
STLStringResizeUninitialized(compressed, MaxCompressedLength(
|
|
uncompressed_length));
|
|
|
|
size_t compressed_length;
|
|
RawCompressFromIOVec(iov, uncompressed_length, string_as_array(compressed),
|
|
&compressed_length);
|
|
compressed->erase(compressed_length);
|
|
return compressed_length;
|
|
}
|
|
|
|
// -----------------------------------------------------------------------
|
|
// Sink interface
|
|
// -----------------------------------------------------------------------
|
|
|
|
// A type that decompresses into a Sink. The template parameter
|
|
// Allocator must export one method "char* Allocate(int size);", which
|
|
// allocates a buffer of "size" and appends that to the destination.
|
|
template <typename Allocator>
|
|
class SnappyScatteredWriter {
|
|
Allocator allocator_;
|
|
|
|
// We need random access into the data generated so far. Therefore
|
|
// we keep track of all of the generated data as an array of blocks.
|
|
// All of the blocks except the last have length kBlockSize.
|
|
std::vector<char*> blocks_;
|
|
size_t expected_;
|
|
|
|
// Total size of all fully generated blocks so far
|
|
size_t full_size_;
|
|
|
|
// Pointer into current output block
|
|
char* op_base_; // Base of output block
|
|
char* op_ptr_; // Pointer to next unfilled byte in block
|
|
char* op_limit_; // Pointer just past block
|
|
// If op < op_limit_min_slop_ then it's safe to unconditionally write
|
|
// kSlopBytes starting at op.
|
|
char* op_limit_min_slop_;
|
|
|
|
inline size_t Size() const { return full_size_ + (op_ptr_ - op_base_); }
|
|
|
|
bool SlowAppend(const char* ip, size_t len);
|
|
bool SlowAppendFromSelf(size_t offset, size_t len);
|
|
|
|
public:
|
|
inline explicit SnappyScatteredWriter(const Allocator& allocator)
|
|
: allocator_(allocator),
|
|
full_size_(0),
|
|
op_base_(NULL),
|
|
op_ptr_(NULL),
|
|
op_limit_(NULL),
|
|
op_limit_min_slop_(NULL) {}
|
|
char* GetOutputPtr() { return op_ptr_; }
|
|
char* GetBase(ptrdiff_t* op_limit_min_slop) {
|
|
*op_limit_min_slop = op_limit_min_slop_ - op_base_;
|
|
return op_base_;
|
|
}
|
|
void SetOutputPtr(char* op) { op_ptr_ = op; }
|
|
|
|
inline void SetExpectedLength(size_t len) {
|
|
assert(blocks_.empty());
|
|
expected_ = len;
|
|
}
|
|
|
|
inline bool CheckLength() const { return Size() == expected_; }
|
|
|
|
// Return the number of bytes actually uncompressed so far
|
|
inline size_t Produced() const { return Size(); }
|
|
|
|
inline bool Append(const char* ip, size_t len, char** op_p) {
|
|
char* op = *op_p;
|
|
size_t avail = op_limit_ - op;
|
|
if (len <= avail) {
|
|
// Fast path
|
|
std::memcpy(op, ip, len);
|
|
*op_p = op + len;
|
|
return true;
|
|
} else {
|
|
op_ptr_ = op;
|
|
bool res = SlowAppend(ip, len);
|
|
*op_p = op_ptr_;
|
|
return res;
|
|
}
|
|
}
|
|
|
|
inline bool TryFastAppend(const char* ip, size_t available, size_t length,
|
|
char** op_p) {
|
|
char* op = *op_p;
|
|
const int space_left = op_limit_ - op;
|
|
if (length <= 16 && available >= 16 + kMaximumTagLength &&
|
|
space_left >= 16) {
|
|
// Fast path, used for the majority (about 95%) of invocations.
|
|
UnalignedCopy128(ip, op);
|
|
*op_p = op + length;
|
|
return true;
|
|
} else {
|
|
return false;
|
|
}
|
|
}
|
|
|
|
inline bool AppendFromSelf(size_t offset, size_t len, char** op_p) {
|
|
char* op = *op_p;
|
|
assert(op >= op_base_);
|
|
// Check if we try to append from before the start of the buffer.
|
|
if (SNAPPY_PREDICT_FALSE((kSlopBytes < 64 && len > kSlopBytes) ||
|
|
static_cast<size_t>(op - op_base_) < offset ||
|
|
op >= op_limit_min_slop_ || offset < len)) {
|
|
if (offset == 0) return false;
|
|
if (SNAPPY_PREDICT_FALSE(static_cast<size_t>(op - op_base_) < offset ||
|
|
op + len > op_limit_)) {
|
|
op_ptr_ = op;
|
|
bool res = SlowAppendFromSelf(offset, len);
|
|
*op_p = op_ptr_;
|
|
return res;
|
|
}
|
|
*op_p = IncrementalCopy(op - offset, op, op + len, op_limit_);
|
|
return true;
|
|
}
|
|
// Fast path
|
|
char* const op_end = op + len;
|
|
std::memmove(op, op - offset, kSlopBytes);
|
|
*op_p = op_end;
|
|
return true;
|
|
}
|
|
|
|
// Called at the end of the decompress. We ask the allocator
|
|
// write all blocks to the sink.
|
|
inline void Flush() { allocator_.Flush(Produced()); }
|
|
};
|
|
|
|
template <typename Allocator>
|
|
bool SnappyScatteredWriter<Allocator>::SlowAppend(const char* ip, size_t len) {
|
|
size_t avail = op_limit_ - op_ptr_;
|
|
while (len > avail) {
|
|
// Completely fill this block
|
|
std::memcpy(op_ptr_, ip, avail);
|
|
op_ptr_ += avail;
|
|
assert(op_limit_ - op_ptr_ == 0);
|
|
full_size_ += (op_ptr_ - op_base_);
|
|
len -= avail;
|
|
ip += avail;
|
|
|
|
// Bounds check
|
|
if (full_size_ + len > expected_) return false;
|
|
|
|
// Make new block
|
|
size_t bsize = std::min<size_t>(kBlockSize, expected_ - full_size_);
|
|
op_base_ = allocator_.Allocate(bsize);
|
|
op_ptr_ = op_base_;
|
|
op_limit_ = op_base_ + bsize;
|
|
op_limit_min_slop_ = op_limit_ - std::min<size_t>(kSlopBytes - 1, bsize);
|
|
|
|
blocks_.push_back(op_base_);
|
|
avail = bsize;
|
|
}
|
|
|
|
std::memcpy(op_ptr_, ip, len);
|
|
op_ptr_ += len;
|
|
return true;
|
|
}
|
|
|
|
template <typename Allocator>
|
|
bool SnappyScatteredWriter<Allocator>::SlowAppendFromSelf(size_t offset,
|
|
size_t len) {
|
|
// Overflow check
|
|
// See SnappyArrayWriter::AppendFromSelf for an explanation of
|
|
// the "offset - 1u" trick.
|
|
const size_t cur = Size();
|
|
if (offset - 1u >= cur) return false;
|
|
if (expected_ - cur < len) return false;
|
|
|
|
// Currently we shouldn't ever hit this path because Compress() chops the
|
|
// input into blocks and does not create cross-block copies. However, it is
|
|
// nice if we do not rely on that, since we can get better compression if we
|
|
// allow cross-block copies and thus might want to change the compressor in
|
|
// the future.
|
|
// TODO Replace this with a properly optimized path. This is not
|
|
// triggered right now. But this is so super slow, that it would regress
|
|
// performance unacceptably if triggered.
|
|
size_t src = cur - offset;
|
|
char* op = op_ptr_;
|
|
while (len-- > 0) {
|
|
char c = blocks_[src >> kBlockLog][src & (kBlockSize - 1)];
|
|
if (!Append(&c, 1, &op)) {
|
|
op_ptr_ = op;
|
|
return false;
|
|
}
|
|
src++;
|
|
}
|
|
op_ptr_ = op;
|
|
return true;
|
|
}
|
|
|
|
class SnappySinkAllocator {
|
|
public:
|
|
explicit SnappySinkAllocator(Sink* dest) : dest_(dest) {}
|
|
~SnappySinkAllocator() {}
|
|
|
|
char* Allocate(int size) {
|
|
Datablock block(new char[size], size);
|
|
blocks_.push_back(block);
|
|
return block.data;
|
|
}
|
|
|
|
// We flush only at the end, because the writer wants
|
|
// random access to the blocks and once we hand the
|
|
// block over to the sink, we can't access it anymore.
|
|
// Also we don't write more than has been actually written
|
|
// to the blocks.
|
|
void Flush(size_t size) {
|
|
size_t size_written = 0;
|
|
for (Datablock& block : blocks_) {
|
|
size_t block_size = std::min<size_t>(block.size, size - size_written);
|
|
dest_->AppendAndTakeOwnership(block.data, block_size,
|
|
&SnappySinkAllocator::Deleter, NULL);
|
|
size_written += block_size;
|
|
}
|
|
blocks_.clear();
|
|
}
|
|
|
|
private:
|
|
struct Datablock {
|
|
char* data;
|
|
size_t size;
|
|
Datablock(char* p, size_t s) : data(p), size(s) {}
|
|
};
|
|
|
|
static void Deleter(void* arg, const char* bytes, size_t size) {
|
|
// TODO: Switch to [[maybe_unused]] when we can assume C++17.
|
|
(void)arg;
|
|
(void)size;
|
|
|
|
delete[] bytes;
|
|
}
|
|
|
|
Sink* dest_;
|
|
std::vector<Datablock> blocks_;
|
|
|
|
// Note: copying this object is allowed
|
|
};
|
|
|
|
size_t UncompressAsMuchAsPossible(Source* compressed, Sink* uncompressed) {
|
|
SnappySinkAllocator allocator(uncompressed);
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SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
|
|
InternalUncompress(compressed, &writer);
|
|
return writer.Produced();
|
|
}
|
|
|
|
bool Uncompress(Source* compressed, Sink* uncompressed) {
|
|
// Read the uncompressed length from the front of the compressed input
|
|
SnappyDecompressor decompressor(compressed);
|
|
uint32_t uncompressed_len = 0;
|
|
if (!decompressor.ReadUncompressedLength(&uncompressed_len)) {
|
|
return false;
|
|
}
|
|
|
|
char c;
|
|
size_t allocated_size;
|
|
char* buf = uncompressed->GetAppendBufferVariable(1, uncompressed_len, &c, 1,
|
|
&allocated_size);
|
|
|
|
const size_t compressed_len = compressed->Available();
|
|
// If we can get a flat buffer, then use it, otherwise do block by block
|
|
// uncompression
|
|
if (allocated_size >= uncompressed_len) {
|
|
SnappyArrayWriter writer(buf);
|
|
bool result = InternalUncompressAllTags(&decompressor, &writer,
|
|
compressed_len, uncompressed_len);
|
|
uncompressed->Append(buf, writer.Produced());
|
|
return result;
|
|
} else {
|
|
SnappySinkAllocator allocator(uncompressed);
|
|
SnappyScatteredWriter<SnappySinkAllocator> writer(allocator);
|
|
return InternalUncompressAllTags(&decompressor, &writer, compressed_len,
|
|
uncompressed_len);
|
|
}
|
|
}
|
|
|
|
} // namespace snappy
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