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Fixed a nasty corruption bug

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recently introduce into the new dictionary mode.
The bug could be reproduced with this command :
./zstreamtest -v --opaqueapi --no-big-tests -s4092 -t639

error was in function ZSTD_count_2segments() :
the beginning of the 2nd segment corresponds to prefixStart
and not the beginning of the current block (istart == src).
This would result in comparing the wrong byte.
This commit is contained in:
Yann Collet
2018-06-01 15:18:32 -07:00
parent 143fc9ff6c
commit 2108decb41
6 changed files with 58 additions and 40 deletions
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10
lib/compress/zstd_double_fast.c
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@@ -126,7 +126,7 @@ size_t ZSTD_compressBlock_doubleFast_generic(
&& ((U32)((prefixLowestIndex-1) - repIndex) >= 3 /* intentional underflow */)
&& (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
const BYTE* repMatchEnd = repIndex < prefixLowestIndex ? dictEnd : iend;
mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, istart) + 4;
mLength = ZSTD_count_2segments(ip+1+4, repMatch+4, iend, repMatchEnd, prefixLowest) + 4;
ip++;
ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
goto _match_stored;
@@ -183,7 +183,7 @@ size_t ZSTD_compressBlock_doubleFast_generic(
continue;
_search_next_long:
{
size_t const hl3 = ZSTD_hashPtr(ip+1, hBitsL, 8);
U32 const matchIndexL3 = hashLong[hl3];
@@ -213,10 +213,10 @@ _search_next_long:
}
}
}
/* if no long +1 match, explore the short match we found */
if (dictMode == ZSTD_dictMatchState && matchIndexS < prefixLowestIndex) {
mLength = ZSTD_count_2segments(ip+4, match+4, iend, dictEnd, istart) + 4;
mLength = ZSTD_count_2segments(ip+4, match+4, iend, dictEnd, prefixLowest) + 4;
offset = (U32)(current - matchIndexS);
while (((ip>anchor) & (match>dictLowest)) && (ip[-1] == match[-1])) { ip--; match--; mLength++; } /* catch up */
} else {
@@ -257,7 +257,7 @@ _match_stored:
if ( ((U32)((prefixLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
&& (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
const BYTE* const repEnd2 = repIndex2 < prefixLowestIndex ? dictEnd : iend;
size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, istart) + 4;
size_t const repLength2 = ZSTD_count_2segments(ip+4, repMatch2+4, iend, repEnd2, prefixLowest) + 4;
U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset; /* swap offset_2 <=> offset_1 */
ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH);
hashSmall[ZSTD_hashPtr(ip, hBitsS, mls)] = current2;