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lossless: 0.5 % compression density improvement

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do not do length 2 matches far away

speedup for non compressible data by inserting two literals at a time
when no matches are found

Change-Id: Ia8e033071f4186bb8148bb2bf13ca37586734aa3
This commit is contained in:
Jyrki Alakuijala 2015-06-23 12:11:51 +00:00 committed by James Zern
parent 7b23b19808
commit 888429f409
1 changed files with 10 additions and 3 deletions
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13
src/enc/backward_references.c
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@ -399,6 +399,7 @@ static int BackwardReferencesLz77(int xsize, int ysize,
VP8LColorCache hashers;
int iter_max, len_for_unit_dist;
const int window_size = GetWindowSizeForHashChain(quality, xsize);
int min_matches = 32;
GetParamsForHashChainFindCopy(quality, low_effort, &iter_max,
&len_for_unit_dist);
@ -415,10 +416,11 @@ static int BackwardReferencesLz77(int xsize, int ysize,
const int max_len = MaxFindCopyLength(pix_count - i);
HashChainFindCopy(hash_chain, i, xsize, argb, max_len, window_size,
iter_max, len_for_unit_dist, &offset, &len);
if (len >= MIN_LENGTH) {
if (len > MIN_LENGTH || (len == MIN_LENGTH && offset <= 512)) {
int offset2 = 0;
int len2 = 0;
int k;
min_matches = 8;
HashChainInsert(hash_chain, &argb[i], i);
if ((len < (max_len >> 2)) && !low_effort) {
// Evaluate Alternative#2: Insert the pixel at 'i' as literal, and code
@ -451,12 +453,17 @@ static int BackwardReferencesLz77(int xsize, int ysize,
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
HashChainInsert(hash_chain, &argb[i], i);
++i;
--min_matches;
if (min_matches <= 0) {
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
HashChainInsert(hash_chain, &argb[i], i);
++i;
}
}
}
while (i < pix_count) {
// Handle the last (two) pixel(s).
// Handle the last pixel(s).
AddSingleLiteral(argb[i], use_color_cache, &hashers, refs);
if (i < (pix_count - 1)) HashChainInsert(hash_chain, &argb[i], i);
++i;
}