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Save bytes in compress by ignoring 0-flag blocks

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Aetias
2024-02-11 08:57:33 +01:00
parent 899b20283e
commit 753fb43f49
1 changed files with 25 additions and 2 deletions
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tools/compress/main.c
+25 -2
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@@ -33,6 +33,7 @@
typedef struct {
uint8_t *pos;
uint32_t totalBytesSaved;
uint8_t flags;
} BlockInfo;
bool FindSubsequence(const uint8_t *buf, const uint8_t *start, const uint8_t *end, size_t *pLen, size_t *pDist) {
@@ -92,13 +93,15 @@ bool Compress(const uint8_t *src, uint8_t *dst, size_t size, uint8_t **pResult,
flagCount = 0;
*pFlags = flags;
bytesSaved -= 1;
flags = 0;
write -= 1;
pFlags = write;
blockInfos[numBlocks].pos = write;
blockInfos[numBlocks].totalBytesSaved = bytesSaved;
blockInfos[numBlocks].flags = flags;
numBlocks++;
flags = 0;
}
}
if (flagCount != 0) {
@@ -114,8 +117,28 @@ bool Compress(const uint8_t *src, uint8_t *dst, size_t size, uint8_t **pResult,
size_t numIdentical = 0;
for (int32_t i = 0; i < numBlocks - 1; ++i) {
if (blockInfos[i].totalBytesSaved == bytesSaved) {
size_t flagBytesSaved = 0;
for (; i >= 0; --i, ++flagBytesSaved) {
// Save more bytes by ignoring blocks that have no length-distance pairs in them
if (blockInfos[i].flags != 0) break;
}
numIdentical = blockInfos[i].pos - write;
write += 1;
// See if it's possible to remove some chunks based on the number of flag bytes saved
flags = blockInfos[i].flags;
for (int32_t j = 0; j < 8 && flagBytesSaved > 0; ++j) {
if ((flags & 0x80) != 0) {
if (flagBytesSaved < 2) break;
numIdentical += 2;
flagBytesSaved -= 2;
} else {
numIdentical += 1;
flagBytesSaved -= 1;
}
flags >>= 1;
}
memcpy(write, src, numIdentical);
while (write[numIdentical] == read[numIdentical]) {
numIdentical += 1;
@@ -125,7 +148,7 @@ bool Compress(const uint8_t *src, uint8_t *dst, size_t size, uint8_t **pResult,
}
free(blockInfos);
*pResult = write;
*pLen = size - (write - dst);
*pLen = writeEnd - write;
*pNumIdentical = numIdentical;
return true;
}