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[lib] Fix off-by-one error in repcode checks

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The repcode checks disallowed repcodes that are equal to `windowLow`.
This is slightly inefficient, but isn't a problem on its own. Together
with the next commit, it cause non-determinism.
This commit is contained in:
Nick Terrell
2021-05-13 17:05:59 -07:00
parent 91c9a247b6
commit 10b35b312b
3 changed files with 8 additions and 8 deletions
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lib/compress/zstd_fast.c
+2 -2
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@@ -418,7 +418,7 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
DEBUGLOG(7, "offset_1 = %u , curr = %u", offset_1, curr);
if ( ( ((U32)((prefixStartIndex-1) - repIndex) >= 3) /* intentional underflow */
& (offset_1 < curr+1 - dictStartIndex) ) /* note: we are searching at curr+1 */
& (offset_1 <= curr+1 - dictStartIndex) ) /* note: we are searching at curr+1 */
&& (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
const BYTE* const repMatchEnd = repIndex < prefixStartIndex ? dictEnd : iend;
size_t const rLength = ZSTD_count_2segments(ip+1 +4, repMatch +4, iend, repMatchEnd, prefixStart) + 4;
@@ -453,7 +453,7 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
U32 const current2 = (U32)(ip-base);
U32 const repIndex2 = current2 - offset_2;
const BYTE* const repMatch2 = repIndex2 < prefixStartIndex ? dictBase + repIndex2 : base + repIndex2;
if ( (((U32)((prefixStartIndex-1) - repIndex2) >= 3) & (offset_2 < curr - dictStartIndex)) /* intentional overflow */
if ( (((U32)((prefixStartIndex-1) - repIndex2) >= 3) & (offset_2 <= curr - dictStartIndex)) /* intentional overflow */
&& (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
const BYTE* const repEnd2 = repIndex2 < prefixStartIndex ? dictEnd : iend;
size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixStart) + 4;