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Correct and clarify repcode offset history logic

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This commit is contained in:
Elliot Gorokhovsky
2022-05-09 21:01:38 -04:00
parent 8bf32de850
commit 97aabc496e
3 changed files with 42 additions and 26 deletions
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lib/compress/zstd_fast.c
+20 -12
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@@ -117,7 +117,7 @@ ZSTD_compressBlock_fast_noDict_generic(
U32 rep_offset1 = rep[0];
U32 rep_offset2 = rep[1];
U32 offsetSaved = 0;
U32 offsetSaved1 = 0, offsetSaved2 = 0;
size_t hash0; /* hash for ip0 */
size_t hash1; /* hash for ip1 */
@@ -141,8 +141,8 @@ ZSTD_compressBlock_fast_noDict_generic(
{ U32 const curr = (U32)(ip0 - base);
U32 const windowLow = ZSTD_getLowestPrefixIndex(ms, curr, cParams->windowLog);
U32 const maxRep = curr - windowLow;
if (rep_offset2 > maxRep) offsetSaved = rep_offset2, rep_offset2 = 0;
if (rep_offset1 > maxRep) offsetSaved = rep_offset1, rep_offset1 = 0;
if (rep_offset2 > maxRep) offsetSaved2 = rep_offset2, rep_offset2 = 0;
if (rep_offset1 > maxRep) offsetSaved1 = rep_offset1, rep_offset1 = 0;
}
/* start each op */
@@ -254,9 +254,13 @@ _cleanup:
* However, it seems to be a meaningful performance hit to try to search
* them. So let's not. */
/* If rep_offset1 started invalid (offsetSaved1 != 0) and became valid (rep_offset1 != 0),
* rotate saved offsets. */
offsetSaved2 = ((offsetSaved1 > 0) & (rep_offset1 > 0)) ? offsetSaved1 : offsetSaved2;
/* save reps for next block */
rep[0] = rep_offset1 ? rep_offset1 : offsetSaved;
rep[1] = rep_offset2 ? rep_offset2 : offsetSaved;
rep[0] = rep_offset1 ? rep_offset1 : offsetSaved1;
rep[1] = rep_offset2 ? rep_offset2 : offsetSaved2;
/* Return the last literals size */
return (size_t)(iend - anchor);
@@ -388,7 +392,6 @@ size_t ZSTD_compressBlock_fast_dictMatchState_generic(
const BYTE* const iend = istart + srcSize;
const BYTE* const ilimit = iend - HASH_READ_SIZE;
U32 offset_1=rep[0], offset_2=rep[1];
U32 offsetSaved = 0;
const ZSTD_matchState_t* const dms = ms->dictMatchState;
const ZSTD_compressionParameters* const dictCParams = &dms->cParams ;
@@ -545,8 +548,8 @@ size_t ZSTD_compressBlock_fast_dictMatchState_generic(
_cleanup:
/* save reps for next block */
rep[0] = offset_1 ? offset_1 : offsetSaved;
rep[1] = offset_2 ? offset_2 : offsetSaved;
rep[0] = offset_1;
rep[1] = offset_2;
/* Return the last literals size */
return (size_t)(iend - anchor);
@@ -603,6 +606,7 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
const BYTE* const iend = istart + srcSize;
const BYTE* const ilimit = iend - 8;
U32 offset_1=rep[0], offset_2=rep[1];
U32 offsetSaved1 = 0, offsetSaved2 = 0;
const BYTE* ip0 = istart;
const BYTE* ip1;
@@ -635,8 +639,8 @@ static size_t ZSTD_compressBlock_fast_extDict_generic(
{ U32 const curr = (U32)(ip0 - base);
U32 const maxRep = curr - dictStartIndex;
if (offset_2 >= maxRep) offset_2 = 0;
if (offset_1 >= maxRep) offset_1 = 0;
if (offset_2 >= maxRep) offsetSaved2 = offset_2, offset_2 = 0;
if (offset_1 >= maxRep) offsetSaved1 = offset_1, offset_1 = 0;
}
/* start each op */
@@ -758,9 +762,13 @@ _cleanup:
* However, it seems to be a meaningful performance hit to try to search
* them. So let's not. */
/* If offset_1 started invalid (offsetSaved1 != 0) and became valid (offset_1 != 0),
* rotate saved offsets. */
offsetSaved2 = ((offsetSaved1 > 0) & (offset_1 > 0)) ? offsetSaved1 : offsetSaved2;
/* save reps for next block */
rep[0] = offset_1 ? offset_1 : rep[0];
rep[1] = offset_2 ? offset_2 : rep[1];
rep[0] = offset_1 ? offset_1 : offsetSaved1;
rep[1] = offset_2 ? offset_2 : offsetSaved2;
/* Return the last literals size */
return (size_t)(iend - anchor);