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Improve documentation regarding various operations in copyBlockSequences

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This commit is contained in:
senhuang42 2020-10-27 10:36:06 -04:00
parent 3a11c7eb03
commit 96b0ff7886
1 changed files with 16 additions and 7 deletions
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23
lib/compress/zstd_compress.c
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@ -2452,10 +2452,13 @@ static void ZSTD_copyBlockSequences(ZSTD_CCtx* zc)
assert(zc->seqCollector.seqIndex + 1 < zc->seqCollector.maxSequences); assert(zc->seqCollector.seqIndex + 1 < zc->seqCollector.maxSequences);
for (i = 0, position = 0; i < seqStoreSeqSize; ++i) { for (i = 0, position = 0; i < seqStoreSeqSize; ++i) {
outSeqs[i].offset = seqStoreSeqs[i].offset - ZSTD_REP_NUM;
outSeqs[i].litLength = seqStoreSeqs[i].litLength; outSeqs[i].litLength = seqStoreSeqs[i].litLength;
outSeqs[i].matchLength = seqStoreSeqs[i].matchLength + MINMATCH; outSeqs[i].matchLength = seqStoreSeqs[i].matchLength + MINMATCH;
/* matchLength and litLength are stored with U16. longLengthPos
* and longLengthID to allow us to represent a single litLength or matchLength
* in the seqStore that has a value larger than U16 (if it exists).
*/
if (i == seqStore->longLengthPos) { if (i == seqStore->longLengthPos) {
if (seqStore->longLengthID == 1) { if (seqStore->longLengthID == 1) {
outSeqs[i].litLength += 0x10000; outSeqs[i].litLength += 0x10000;
@ -2465,14 +2468,15 @@ static void ZSTD_copyBlockSequences(ZSTD_CCtx* zc)
} }
/* Repcode handling: /* Repcode handling:
* See docs/format.md for more detail about repeat offset codes
* If litLength != 0: * If litLength != 0:
* rep == 1 --> offset == repeat offset 1 * rep == 1 --> offset == repeat_offset_1
* rep == 2 --> offset == repeat offset 2 * rep == 2 --> offset == repeat_offset_2
* rep == 3 --> offset == repeat offset 3 * rep == 3 --> offset == repeat_offset_3
* If litLength == 0: * If litLength == 0:
* rep == 1 --> offset == repeat offset 2 * rep == 1 --> offset == repeat_offset_2
* rep == 2 --> offset == repeat offset 3 * rep == 2 --> offset == repeat_offset_3
* rep == 3 --> offset == repeat offset 1 - 1 * rep == 3 --> offset == repeat_offset_1 - 1
*/ */
if (seqStoreSeqs[i].offset <= ZSTD_REP_NUM) { if (seqStoreSeqs[i].offset <= ZSTD_REP_NUM) {
outSeqs[i].rep = seqStoreSeqs[i].offset; outSeqs[i].rep = seqStoreSeqs[i].offset;
@ -2486,10 +2490,15 @@ static void ZSTD_copyBlockSequences(ZSTD_CCtx* zc)
} }
} }
assert(repIdx >= -3); assert(repIdx >= -3);
/* Use default repcodes if repcode references an offset that doesn't exist yet
* This can only occur within the first two sequences.
*/
outSeqs[i].offset = repIdx >= 0 ? outSeqs[repIdx].offset : repStartValue[-repIdx - 1]; outSeqs[i].offset = repIdx >= 0 ? outSeqs[repIdx].offset : repStartValue[-repIdx - 1];
if (outSeqs[i].rep == 3 && outSeqs[i].litLength == 0) { if (outSeqs[i].rep == 3 && outSeqs[i].litLength == 0) {
--outSeqs[i].offset; --outSeqs[i].offset;
} }
} else {
outSeqs[i].offset = seqStoreSeqs[i].offset - ZSTD_REP_NUM;
} }
position += outSeqs[i].litLength + outSeqs[i].matchLength; position += outSeqs[i].litLength + outSeqs[i].matchLength;
} }