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When we compare the number of bytes produced with the offset for a 

backreference, make the signedness of the bytes produced clear,
by sticking it into a size_t. This avoids a signed/unsigned compare
warning from MSVC (public issue 71), and also is slightly clearer.

Since the line is now so long the explanatory comment about the -1u
trick has to go somewhere else anyway, I used the opportunity to
explain it in slightly more detail.

This is a purely stylistic change; the emitted assembler from GCC
is identical.

R=jeff


git-svn-id: https://snappy.googlecode.com/svn/trunk@79 03e5f5b5-db94-4691-08a0-1a8bf15f6143
This commit is contained in:
snappy.mirrorbot@gmail.com 2013-07-29 11:06:44 +00:00
parent 2f0aaf8631
commit 7c3c01df77
1 changed files with 13 additions and 2 deletions
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15
snappy.cc
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@ -1185,7 +1185,16 @@ class SnappyArrayWriter {
char* op = op_;
const size_t space_left = op_limit_ - op;
if (op - base_ <= offset - 1u) { // -1u catches offset==0
// Check if we try to append from before the start of the buffer.
// Normally this would just be a check for "produced < offset",
// but "produced <= offset - 1u" is equivalent for every case
// except the one where offset==0, where the right side will wrap around
// to a very big number. This is convenient, as offset==0 is another
// invalid case that we also want to catch, so that we do not go
// into an infinite loop.
assert(op >= base_);
size_t produced = op - base_;
if (produced <= offset - 1u) {
return false;
}
if (len <= 16 && offset >= 8 && space_left >= 16) {
@ -1255,7 +1264,9 @@ class SnappyDecompressionValidator {
return false;
}
inline bool AppendFromSelf(size_t offset, size_t len) {
if (produced_ <= offset - 1u) return false; // -1u catches offset==0
// See SnappyArrayWriter::AppendFromSelf for an explanation of
// the "offset - 1u" trick.
if (produced_ <= offset - 1u) return false;
produced_ += len;
return produced_ <= expected_;
}