summaryrefslogtreecommitdiffstats
path: root/lib/lz4hc.c
diff options
context:
space:
mode:
Diffstat (limited to 'lib/lz4hc.c')
-rw-r--r--lib/lz4hc.c65
1 files changed, 45 insertions, 20 deletions
diff --git a/lib/lz4hc.c b/lib/lz4hc.c
index a0b8c48..596888a 100644
--- a/lib/lz4hc.c
+++ b/lib/lz4hc.c
@@ -218,6 +218,16 @@ LZ4HC_reverseCountPattern(const BYTE* ip, const BYTE* const iLow, U32 pattern)
return (unsigned)(iStart - ip);
}
+/* LZ4HC_protectDictEnd() :
+ * Checks if the match is in the last 3 bytes of the dictionary, so reading the
+ * 4 byte MINMATCH would overflow.
+ * @returns true if the match index is okay.
+ */
+static int LZ4HC_protectDictEnd(U32 const dictLimit, U32 const matchIndex)
+{
+ return ((U32)((dictLimit - 1) - matchIndex) >= 3);
+}
+
typedef enum { rep_untested, rep_not, rep_confirmed } repeat_state_e;
typedef enum { favorCompressionRatio=0, favorDecompressionSpeed } HCfavor_e;
@@ -304,7 +314,7 @@ LZ4HC_InsertAndGetWiderMatch (
if (matchIndex + (U32)longest <= ipIndex) {
U32 distanceToNextMatch = 1;
int pos;
- for (pos = 0; pos <= longest - MINMATCH; pos++) {
+ for (pos = 0; pos <= longest - MINMATCH; ++pos) {
U32 const candidateDist = DELTANEXTU16(chainTable, matchIndex + (U32)pos);
if (candidateDist > distanceToNextMatch) {
distanceToNextMatch = candidateDist;
@@ -314,7 +324,8 @@ LZ4HC_InsertAndGetWiderMatch (
if (distanceToNextMatch > matchIndex) break; /* avoid overflow */
matchIndex -= distanceToNextMatch;
continue;
- } } }
+ }
+ } }
{ U32 const distNextMatch = DELTANEXTU16(chainTable, matchIndex);
if (patternAnalysis && distNextMatch==1 && matchChainPos==0) {
@@ -328,7 +339,8 @@ LZ4HC_InsertAndGetWiderMatch (
} else {
repeat = rep_not;
} }
- if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex) ) {
+ if ( (repeat == rep_confirmed) && (matchCandidateIdx >= lowestMatchIndex)
+ && LZ4HC_protectDictEnd(dictLimit, matchCandidateIdx) ) {
const int extDict = matchCandidateIdx < dictLimit;
const BYTE* const matchPtr = (extDict ? dictBase : base) + matchCandidateIdx;
if (LZ4_read32(matchPtr) == pattern) { /* good candidate */
@@ -348,27 +360,40 @@ LZ4HC_InsertAndGetWiderMatch (
}
/* Limit backLength not go further than lowestMatchIndex */
backLength = matchCandidateIdx - MAX(matchCandidateIdx - (U32)backLength, lowestMatchIndex);
+ assert(matchCandidateIdx - backLength >= lowestMatchIndex);
currentSegmentLength = backLength + forwardPatternLength;
-
+ /* Adjust to end of pattern if the source pattern fits, otherwise the beginning of the pattern */
if ( (currentSegmentLength >= srcPatternLength) /* current pattern segment large enough to contain full srcPatternLength */
&& (forwardPatternLength <= srcPatternLength) ) { /* haven't reached this position yet */
- matchIndex = matchCandidateIdx + (U32)forwardPatternLength - (U32)srcPatternLength; /* best position, full pattern, might be followed by more match */
+ U32 const newMatchIndex = matchCandidateIdx + (U32)forwardPatternLength - (U32)srcPatternLength; /* best position, full pattern, might be followed by more match */
+ if (LZ4HC_protectDictEnd(dictLimit, newMatchIndex))
+ matchIndex = newMatchIndex;
+ else {
+ /* Can only happen if started in the prefix */
+ assert(newMatchIndex >= dictLimit - 3 && newMatchIndex < dictLimit && !extDict);
+ matchIndex = dictLimit;
+ }
} else {
- matchIndex = matchCandidateIdx - (U32)backLength; /* farthest position in current segment, will find a match of length currentSegmentLength + maybe some back */
- if (lookBackLength==0) { /* no back possible */
- size_t const maxML = MIN(currentSegmentLength, srcPatternLength);
- if ((size_t)longest < maxML) {
- assert(base + matchIndex < ip);
- if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break;
- assert(maxML < 2 GB);
- longest = (int)maxML;
- *matchpos = base + matchIndex; /* virtual pos, relative to ip, to retrieve offset */
- *startpos = ip;
- }
- { U32 const distToNextPattern = DELTANEXTU16(chainTable, matchIndex);
- if (distToNextPattern > matchIndex) break; /* avoid overflow */
- matchIndex -= distToNextPattern;
- } } } }
+ U32 const newMatchIndex = matchCandidateIdx - (U32)backLength; /* farthest position in current segment, will find a match of length currentSegmentLength + maybe some back */
+ if (!LZ4HC_protectDictEnd(dictLimit, newMatchIndex)) {
+ assert(newMatchIndex >= dictLimit - 3 && newMatchIndex < dictLimit && !extDict);
+ matchIndex = dictLimit;
+ } else {
+ matchIndex = newMatchIndex;
+ if (lookBackLength==0) { /* no back possible */
+ size_t const maxML = MIN(currentSegmentLength, srcPatternLength);
+ if ((size_t)longest < maxML) {
+ assert(base + matchIndex < ip);
+ if (ip - (base+matchIndex) > LZ4_DISTANCE_MAX) break;
+ assert(maxML < 2 GB);
+ longest = (int)maxML;
+ *matchpos = base + matchIndex; /* virtual pos, relative to ip, to retrieve offset */
+ *startpos = ip;
+ }
+ { U32 const distToNextPattern = DELTANEXTU16(chainTable, matchIndex);
+ if (distToNextPattern > matchIndex) break; /* avoid overflow */
+ matchIndex -= distToNextPattern;
+ } } } } }
continue;
} }
} } /* PA optimization */