From 7c3c01df77e191ad1f8377448961fe88db2802e9 Mon Sep 17 00:00:00 2001 From: "snappy.mirrorbot@gmail.com" Date: Mon, 29 Jul 2013 11:06:44 +0000 Subject: [PATCH] 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 --- snappy.cc | 15 +++++++++++++-- 1 file changed, 13 insertions(+), 2 deletions(-) diff --git a/snappy.cc b/snappy.cc index 341c9a0..f8d0d23 100644 --- a/snappy.cc +++ b/snappy.cc @@ -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_; }