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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_lazy.c
+4 -4
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@@ -1995,7 +1995,7 @@ size_t ZSTD_compressBlock_lazy_extDict_generic(
const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
const BYTE* const repMatch = repBase + repIndex;
if ( ((U32)((dictLimit-1) - repIndex) >= 3) /* intentional overflow */
& (offset_1 < curr+1 - windowLow) ) /* note: we are searching at curr+1 */
& (offset_1 <= curr+1 - windowLow) ) /* note: we are searching at curr+1 */
if (MEM_read32(ip+1) == MEM_read32(repMatch)) {
/* repcode detected we should take it */
const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;
@@ -2027,7 +2027,7 @@ size_t ZSTD_compressBlock_lazy_extDict_generic(
const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
const BYTE* const repMatch = repBase + repIndex;
if ( ((U32)((dictLimit-1) - repIndex) >= 3) /* intentional overflow : do not test positions overlapping 2 memory segments */
& (offset_1 < curr - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
& (offset_1 <= curr - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
if (MEM_read32(ip) == MEM_read32(repMatch)) {
/* repcode detected */
const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;
@@ -2059,7 +2059,7 @@ size_t ZSTD_compressBlock_lazy_extDict_generic(
const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
const BYTE* const repMatch = repBase + repIndex;
if ( ((U32)((dictLimit-1) - repIndex) >= 3) /* intentional overflow : do not test positions overlapping 2 memory segments */
& (offset_1 < curr - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
& (offset_1 <= curr - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
if (MEM_read32(ip) == MEM_read32(repMatch)) {
/* repcode detected */
const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;
@@ -2106,7 +2106,7 @@ _storeSequence:
const BYTE* const repBase = repIndex < dictLimit ? dictBase : base;
const BYTE* const repMatch = repBase + repIndex;
if ( ((U32)((dictLimit-1) - repIndex) >= 3) /* intentional overflow : do not test positions overlapping 2 memory segments */
& (offset_2 < repCurrent - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
& (offset_2 <= repCurrent - windowLow) ) /* equivalent to `curr > repIndex >= windowLow` */
if (MEM_read32(ip) == MEM_read32(repMatch)) {
/* repcode detected we should take it */
const BYTE* const repEnd = repIndex < dictLimit ? dictEnd : iend;