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Use New Index Invariant to Simplify Conditionals

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This commit is contained in:
W. Felix Handte 2018-05-10 17:18:08 -04:00
parent 2d598e6fed
commit 1a7b34ef28
1 changed files with 15 additions and 16 deletions
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31
lib/compress/zstd_fast.c
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@ -74,16 +74,18 @@ size_t ZSTD_compressBlock_fast_generic(
const U32 dictIndexDelta = dictMode == ZSTD_dictMatchState ? const U32 dictIndexDelta = dictMode == ZSTD_dictMatchState ?
localLowestIndex - (U32)(dictEnd - dictBase) : localLowestIndex - (U32)(dictEnd - dictBase) :
0; 0;
ptrdiff_t dictLowestLocalIndex = dictMode == ZSTD_dictMatchState ?
lowestDictIndex + dictIndexDelta :
localLowestIndex;
assert(dictMode == ZSTD_noDict || dictMode == ZSTD_dictMatchState); assert(dictMode == ZSTD_noDict || dictMode == ZSTD_dictMatchState);
/* otherwise, we would get index underflow when translating a dict index
* into a local index */
assert(dictMode != ZSTD_dictMatchState
|| localLowestIndex >= (U32)(dictEnd - dictBase));
/* init */ /* init */
ip += (dictMode == ZSTD_noDict && ip == localLowest); ip += (dictMode == ZSTD_noDict && ip == localLowest);
{ U32 const maxRep = dictMode == ZSTD_dictMatchState ? { U32 const maxRep = dictMode == ZSTD_dictMatchState ?
(U32)(ip - dictLowest) : (U32)(ip - localLowest + dictEnd - dictLowest) :
(U32)(ip - localLowest); (U32)(ip - localLowest);
if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0; if (offset_2 > maxRep) offsetSaved = offset_2, offset_2 = 0;
if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0; if (offset_1 > maxRep) offsetSaved = offset_1, offset_1 = 0;
@ -96,23 +98,22 @@ size_t ZSTD_compressBlock_fast_generic(
U32 const current = (U32)(ip-base); U32 const current = (U32)(ip-base);
U32 const matchIndex = hashTable[h]; U32 const matchIndex = hashTable[h];
const BYTE* match = base + matchIndex; const BYTE* match = base + matchIndex;
const ptrdiff_t repIndex = (ptrdiff_t)current + 1 - offset_1; const U32 repIndex = current + 1 - offset_1;
const BYTE* repBase = (dictMode == ZSTD_dictMatchState const BYTE* repBase = (dictMode == ZSTD_dictMatchState
&& repIndex < (ptrdiff_t)localLowestIndex) ? && repIndex < localLowestIndex) ?
dictBase - dictIndexDelta : base; dictBase - dictIndexDelta : base;
const BYTE* repMatch = repBase + repIndex; const BYTE* repMatch = repBase + repIndex;
hashTable[h] = current; /* update hash table */ hashTable[h] = current; /* update hash table */
if (dictMode == ZSTD_dictMatchState if (dictMode == ZSTD_dictMatchState
&& (((U32)((localLowestIndex-1) - repIndex) >= 3 /* intentional underflow */) && ((U32)((localLowestIndex-1) - repIndex) >= 3 /* intentional underflow */)
& (repIndex > dictLowestLocalIndex))
&& (MEM_read32(repMatch) == MEM_read32(ip+1)) ) { && (MEM_read32(repMatch) == MEM_read32(ip+1)) ) {
const BYTE* repMatchEnd = repIndex < (ptrdiff_t)localLowestIndex ? dictEnd : iend; const BYTE* repMatchEnd = repIndex < localLowestIndex ? 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, istart) + 4;
ip++; ip++;
ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH); ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
} else if ( dictMode == ZSTD_noDict } else if ( dictMode == ZSTD_noDict
&& (offset_1 > 0) & (MEM_read32(ip+1-offset_1) == MEM_read32(ip+1))) { && ((offset_1 > 0) & (MEM_read32(ip+1-offset_1) == MEM_read32(ip+1)))) {
mLength = ZSTD_count(ip+1+4, ip+1+4-offset_1, iend) + 4; mLength = ZSTD_count(ip+1+4, ip+1+4-offset_1, iend) + 4;
ip++; ip++;
ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH); ZSTD_storeSeq(seqStore, ip-anchor, anchor, 0, mLength-MINMATCH);
@ -167,15 +168,14 @@ size_t ZSTD_compressBlock_fast_generic(
if (dictMode == ZSTD_dictMatchState) { if (dictMode == ZSTD_dictMatchState) {
while (ip <= ilimit) { while (ip <= ilimit) {
U32 const current2 = (U32)(ip-base); U32 const current2 = (U32)(ip-base);
ptrdiff_t const repIndex2 = (ptrdiff_t)current2 - offset_2; U32 const repIndex2 = current2 - offset_2;
const BYTE* repMatch2 = dictMode == ZSTD_dictMatchState const BYTE* repMatch2 = dictMode == ZSTD_dictMatchState
&& repIndex2 < (ptrdiff_t)localLowestIndex ? && repIndex2 < localLowestIndex ?
dictBase - dictIndexDelta + repIndex2 : dictBase - dictIndexDelta + repIndex2 :
base + repIndex2; base + repIndex2;
if ( (((U32)((localLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */) if ( ((U32)((localLowestIndex-1) - (U32)repIndex2) >= 3 /* intentional overflow */)
& (repIndex2 > dictLowestLocalIndex))
&& (MEM_read32(repMatch2) == MEM_read32(ip)) ) { && (MEM_read32(repMatch2) == MEM_read32(ip)) ) {
const BYTE* const repEnd2 = repIndex2 < (ptrdiff_t)localLowestIndex ? dictEnd : iend; const BYTE* const repEnd2 = repIndex2 < localLowestIndex ? 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, istart) + 4;
U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset; /* swap offset_2 <=> offset_1 */ U32 tmpOffset = offset_2; offset_2 = offset_1; offset_1 = tmpOffset; /* swap offset_2 <=> offset_1 */
ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH); ZSTD_storeSeq(seqStore, 0, anchor, 0, repLength2-MINMATCH);
@ -190,7 +190,6 @@ size_t ZSTD_compressBlock_fast_generic(
if (dictMode == ZSTD_noDict) { if (dictMode == ZSTD_noDict) {
while ( (ip <= ilimit) while ( (ip <= ilimit)
&& (ip - offset_2 >= istart)
&& ( (offset_2>0) && ( (offset_2>0)
& (MEM_read32(ip) == MEM_read32(ip - offset_2)) )) { & (MEM_read32(ip) == MEM_read32(ip - offset_2)) )) {
/* store sequence */ /* store sequence */