rocksdb/util/coding.cc

// Copyright (c) 2011 The LevelDB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file. See the AUTHORS file for names of contributors.

#include "util/coding.h"

#include <algorithm>

namespace leveldb {

void EncodeFixed32(char* buf, uint32_t value) {
#if __BYTE_ORDER == __LITTLE_ENDIAN
  memcpy(buf, &value, sizeof(value));
#else
  buf[0] = value & 0xff;
  buf[1] = (value >> 8) & 0xff;
  buf[2] = (value >> 16) & 0xff;
  buf[3] = (value >> 24) & 0xff;
#endif
}

void EncodeFixed64(char* buf, uint64_t value) {
#if __BYTE_ORDER == __LITTLE_ENDIAN
  memcpy(buf, &value, sizeof(value));
#else
  buf[0] = value & 0xff;
  buf[1] = (value >> 8) & 0xff;
  buf[2] = (value >> 16) & 0xff;
  buf[3] = (value >> 24) & 0xff;
  buf[4] = (value >> 32) & 0xff;
  buf[5] = (value >> 40) & 0xff;
  buf[6] = (value >> 48) & 0xff;
  buf[7] = (value >> 56) & 0xff;
#endif
}

void PutFixed32(std::string* dst, uint32_t value) {
  char buf[sizeof(value)];
  EncodeFixed32(buf, value);
  dst->append(buf, sizeof(buf));
}

void PutFixed64(std::string* dst, uint64_t value) {
  char buf[sizeof(value)];
  EncodeFixed64(buf, value);
  dst->append(buf, sizeof(buf));
}

char* EncodeVarint32(char* dst, uint32_t v) {
  // Operate on characters as unsigneds
  unsigned char* ptr = reinterpret_cast<unsigned char*>(dst);
  static const int B = 128;
  if (v < (1<<7)) {
    *(ptr++) = v;
  } else if (v < (1<<14)) {
    *(ptr++) = v | B;
    *(ptr++) = v>>7;
  } else if (v < (1<<21)) {
    *(ptr++) = v | B;
    *(ptr++) = (v>>7) | B;
    *(ptr++) = v>>14;
  } else if (v < (1<<28)) {
    *(ptr++) = v | B;
    *(ptr++) = (v>>7) | B;
    *(ptr++) = (v>>14) | B;
    *(ptr++) = v>>21;
  } else {
    *(ptr++) = v | B;
    *(ptr++) = (v>>7) | B;
    *(ptr++) = (v>>14) | B;
    *(ptr++) = (v>>21) | B;
    *(ptr++) = v>>28;
  }
  return reinterpret_cast<char*>(ptr);
}

void PutVarint32(std::string* dst, uint32_t v) {
  char buf[5];
  char* ptr = EncodeVarint32(buf, v);
  dst->append(buf, ptr - buf);
}

char* EncodeVarint64(char* dst, uint64_t v) {
  static const unsigned int B = 128;
  unsigned char* ptr = reinterpret_cast<unsigned char*>(dst);
  while (v >= B) {
    *(ptr++) = (v & (B-1)) | B;
    v >>= 7;
  }
  *(ptr++) = static_cast<unsigned char>(v);
  return reinterpret_cast<char*>(ptr);
}

void PutVarint64(std::string* dst, uint64_t v) {
  char buf[10];
  char* ptr = EncodeVarint64(buf, v);
  dst->append(buf, ptr - buf);
}

void PutLengthPrefixedSlice(std::string* dst, const Slice& value) {
  PutVarint32(dst, value.size());
  dst->append(value.data(), value.size());
}

int VarintLength(uint64_t v) {
  int len = 1;
  while (v >= 128) {
    v >>= 7;
    len++;
  }
  return len;
}

const char* GetVarint32PtrFallback(const char* p,
                                   const char* limit,
                                   uint32_t* value) {
  uint32_t result = 0;
  for (uint32_t shift = 0; shift <= 28 && p < limit; shift += 7) {
    uint32_t byte = *(reinterpret_cast<const unsigned char*>(p));
    p++;
    if (byte & 128) {
      // More bytes are present
      result |= ((byte & 127) << shift);
    } else {
      result |= (byte << shift);
      *value = result;
      return reinterpret_cast<const char*>(p);
    }
  }
  return nullptr;
}

bool GetVarint32(Slice* input, uint32_t* value) {
  const char* p = input->data();
  const char* limit = p + input->size();
  const char* q = GetVarint32Ptr(p, limit, value);
  if (q == nullptr) {
    return false;
  } else {
    *input = Slice(q, limit - q);
    return true;
  }
}

const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* value) {
  uint64_t result = 0;
  for (uint32_t shift = 0; shift <= 63 && p < limit; shift += 7) {
    uint64_t byte = *(reinterpret_cast<const unsigned char*>(p));
    p++;
    if (byte & 128) {
      // More bytes are present
      result |= ((byte & 127) << shift);
    } else {
      result |= (byte << shift);
      *value = result;
      return reinterpret_cast<const char*>(p);
    }
  }
  return nullptr;
}

bool GetVarint64(Slice* input, uint64_t* value) {
  const char* p = input->data();
  const char* limit = p + input->size();
  const char* q = GetVarint64Ptr(p, limit, value);
  if (q == nullptr) {
    return false;
  } else {
    *input = Slice(q, limit - q);
    return true;
  }
}

const char* GetLengthPrefixedSlice(const char* p, const char* limit,
                                   Slice* result) {
  uint32_t len;
  p = GetVarint32Ptr(p, limit, &len);
  if (p == nullptr) return nullptr;
  if (p + len > limit) return nullptr;
  *result = Slice(p, len);
  return p + len;
}

bool GetLengthPrefixedSlice(Slice* input, Slice* result) {
  uint32_t len;
  if (GetVarint32(input, &len) &&
      input->size() >= len) {
    *result = Slice(input->data(), len);
    input->remove_prefix(len);
    return true;
  } else {
    return false;
  }
}

void BitStreamPutInt(char* dst, size_t dstlen, size_t offset,
                     uint32_t bits, uint64_t value) {
  assert((offset + bits + 7)/8 <= dstlen);
  assert(bits <= 64);

  unsigned char* ptr = reinterpret_cast<unsigned char*>(dst);

  size_t byteOffset = offset / 8;
  size_t bitOffset = offset % 8;

  // This prevents unused variable warnings when compiling.
#ifndef NDEBUG
  // Store truncated value.
  uint64_t origValue = (bits < 64)?(value & (((uint64_t)1 << bits) - 1)):value;
  uint32_t origBits = bits;
#endif

  while (bits > 0) {
    size_t bitsToGet = std::min<size_t>(bits, 8 - bitOffset);
    unsigned char mask = ((1 << bitsToGet) - 1);

    ptr[byteOffset] = (ptr[byteOffset] & ~(mask << bitOffset)) +
                      ((value & mask) << bitOffset);

    value >>= bitsToGet;
    byteOffset += 1;
    bitOffset = 0;
    bits -= bitsToGet;
  }

  assert(origValue == BitStreamGetInt(dst, dstlen, offset, origBits));
}

uint64_t BitStreamGetInt(const char* src, size_t srclen, size_t offset,
                         uint32_t bits) {
  assert((offset + bits + 7)/8 <= srclen);
  assert(bits <= 64);

  const unsigned char* ptr = reinterpret_cast<const unsigned char*>(src);

  uint64_t result = 0;

  size_t byteOffset = offset / 8;
  size_t bitOffset = offset % 8;
  size_t shift = 0;

  while (bits > 0) {
    size_t bitsToGet = std::min<size_t>(bits, 8 - bitOffset);
    unsigned char mask = ((1 << bitsToGet) - 1);

    result += (uint64_t)((ptr[byteOffset] >> bitOffset) & mask) << shift;

    shift += bitsToGet;
    byteOffset += 1;
    bitOffset = 0;
    bits -= bitsToGet;
  }

  return result;
}

void BitStreamPutInt(std::string* dst, size_t offset, uint32_t bits,
                     uint64_t value) {
  assert((offset + bits + 7)/8 <= dst->size());

  const size_t kTmpBufLen = sizeof(value) + 1;
  char tmpBuf[kTmpBufLen];

  // Number of bytes of tmpBuf being used
  const size_t kUsedBytes = (offset%8 + bits)/8;

  // Copy relevant parts of dst to tmpBuf
  for (size_t idx = 0; idx <= kUsedBytes; ++idx) {
    tmpBuf[idx] = (*dst)[offset/8 + idx];
  }

  BitStreamPutInt(tmpBuf, kTmpBufLen, offset%8, bits, value);

  // Copy tmpBuf back to dst
  for (size_t idx = 0; idx <= kUsedBytes; ++idx) {
    (*dst)[offset/8 + idx] = tmpBuf[idx];
  }

  // Do the check here too as we are working with a buffer.
  assert(((bits < 64)?(value & (((uint64_t)1 << bits) - 1)):value) ==
         BitStreamGetInt(dst, offset, bits));
}

uint64_t BitStreamGetInt(const std::string* src, size_t offset,
                         uint32_t bits) {
  return BitStreamGetInt(src->data(), src->size(), offset, bits);
}

uint64_t BitStreamGetInt(const Slice* src, size_t offset,
                         uint32_t bits) {
  return BitStreamGetInt(src->data(), src->size(), offset, bits);
}

}  // namespace leveldb