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Small optimization to the cost model

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emmanuel-marty 2019-04-13 12:33:39 +02:00
parent 4913fe5d48
commit aa5dbe283d
1 changed files with 11 additions and 22 deletions
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33
src/shrink.c
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@ -25,6 +25,7 @@
* *
* Inspired by LZ4 by Yann Collet. https://github.com/lz4/lz4 * Inspired by LZ4 by Yann Collet. https://github.com/lz4/lz4
* With ideas from Lizard by Przemyslaw Skibinski and Yann Collet. https://github.com/inikep/lizard * With ideas from Lizard by Przemyslaw Skibinski and Yann Collet. https://github.com/inikep/lizard
* Also with ideas from smallz4 by Stephan Brumme. https://create.stephan-brumme.com/smallz4/
* *
*/ */
@ -495,15 +496,18 @@ static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStart
int i; int i;
cost[nEndOffset - 1] = 1; cost[nEndOffset - 1] = 1;
nLastLiteralsOffset = nEndOffset - 1; nLastLiteralsOffset = nEndOffset;
for (i = nEndOffset - 2; i != (nStartOffset - 1); i--) { for (i = nEndOffset - 2; i != (nStartOffset - 1); i--) {
int nBestCost, nBestMatchLen, nBestMatchOffset; int nBestCost, nBestMatchLen, nBestMatchOffset;
int nLiteralsLen = nLastLiteralsOffset - i; int nLiteralsLen = nLastLiteralsOffset - i;
nBestCost = 1 + cost[i + 1] + lzsa_get_literals_varlen_size(nLiteralsLen); nBestCost = 1 + cost[i + 1];
if (nLiteralsLen > 1) if (nLiteralsLen == LITERALS_RUN_LEN || nLiteralsLen == (LITERALS_RUN_LEN + 254) || nLiteralsLen == (LITERALS_RUN_LEN + 510)) {
nBestCost -= lzsa_get_literals_varlen_size(nLiteralsLen - 1); /* Add to the cost of encoding literals as their number crosses a variable length encoding boundary.
* The cost automatically accumulates down the chain. */
nBestCost++;
}
nBestMatchLen = 0; nBestMatchLen = 0;
nBestMatchOffset = 0; nBestMatchOffset = 0;
@ -516,17 +520,12 @@ static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStart
if (pMatch[m].length >= LEAVE_ALONE_MATCH_SIZE) { if (pMatch[m].length >= LEAVE_ALONE_MATCH_SIZE) {
int nCurCost; int nCurCost;
int nMatchLen = pMatch[m].length; int nMatchLen = pMatch[m].length;
int nRemainingLiteralsLen = nLastLiteralsOffset - (i + nMatchLen);
if (nRemainingLiteralsLen < 0) nRemainingLiteralsLen = 0;
if ((i + nMatchLen) > (nEndOffset - LAST_LITERALS)) if ((i + nMatchLen) > (nEndOffset - LAST_LITERALS))
nMatchLen = nEndOffset - LAST_LITERALS - i; nMatchLen = nEndOffset - LAST_LITERALS - i;
nCurCost = 1 + lzsa_get_literals_varlen_size(nRemainingLiteralsLen) + nMatchOffsetSize + lzsa_get_match_varlen_size(nMatchLen - MIN_MATCH_SIZE); nCurCost = 1 + nMatchOffsetSize + lzsa_get_match_varlen_size(nMatchLen - MIN_MATCH_SIZE);
nCurCost += cost[i + nMatchLen]; nCurCost += cost[i + nMatchLen];
if (nRemainingLiteralsLen > 1)
nCurCost -= lzsa_get_literals_varlen_size(nRemainingLiteralsLen - 1);
if (nBestCost >= nCurCost) { if (nBestCost >= nCurCost) {
nBestCost = nCurCost; nBestCost = nCurCost;
@ -548,14 +547,9 @@ static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStart
for (k = MIN_MATCH_SIZE; k < nMatchRunLen; k++) { for (k = MIN_MATCH_SIZE; k < nMatchRunLen; k++) {
int nCurCost; int nCurCost;
int nRemainingLiteralsLen = nLastLiteralsOffset - (i + k);
if (nRemainingLiteralsLen < 0) nRemainingLiteralsLen = 0; nCurCost = 1 + nMatchOffsetSize /* no extra match len bytes */;
nCurCost = 1 + lzsa_get_literals_varlen_size(nRemainingLiteralsLen) + nMatchOffsetSize /* no extra match len bytes */;
nCurCost += cost[i + k]; nCurCost += cost[i + k];
if (nRemainingLiteralsLen > 1)
nCurCost -= lzsa_get_literals_varlen_size(nRemainingLiteralsLen - 1);
if (nBestCost >= nCurCost) { if (nBestCost >= nCurCost) {
nBestCost = nCurCost; nBestCost = nCurCost;
@ -566,14 +560,9 @@ static void lzsa_optimize_matches(lsza_compressor *pCompressor, const int nStart
for (; k <= nMatchLen; k++) { for (; k <= nMatchLen; k++) {
int nCurCost; int nCurCost;
int nRemainingLiteralsLen = nLastLiteralsOffset - (i + k);
if (nRemainingLiteralsLen < 0) nRemainingLiteralsLen = 0; nCurCost = 1 + nMatchOffsetSize + lzsa_get_match_varlen_size(k - MIN_MATCH_SIZE);
nCurCost = 1 + lzsa_get_literals_varlen_size(nRemainingLiteralsLen) + nMatchOffsetSize + lzsa_get_match_varlen_size(k - MIN_MATCH_SIZE);
nCurCost += cost[i + k]; nCurCost += cost[i + k];
if (nRemainingLiteralsLen > 1)
nCurCost -= lzsa_get_literals_varlen_size(nRemainingLiteralsLen - 1);
if (nBestCost >= nCurCost) { if (nBestCost >= nCurCost) {
nBestCost = nCurCost; nBestCost = nCurCost;