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Small LZ77 speedups.

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The most common conditions are re-ordered and cached.

iter_min was recently introduced to make sure enough iterations
are made in cases where there are many matches (mostly uniform regions).
Now that those are properly analyzed, it becomes useless.

Change-Id: Id3010ee4ec66b84d602fcb926f91eb9155ad27f4
This commit is contained in:
Vincent Rabaud 2016-09-22 14:03:25 +02:00
parent a2fe9bf404
commit 5f1caf2987
1 changed files with 9 additions and 14 deletions
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23
src/enc/backward_references.c
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@ -247,7 +247,6 @@ int VP8LHashChainFill(VP8LHashChain* const p, int quality,
int low_effort) {
const int size = xsize * ysize;
const int iter_max = GetMaxItersForQuality(quality);
const int iter_min = iter_max - quality / 10;
const uint32_t window_size = GetWindowSizeForHashChain(quality, xsize);
int pos;
int argb_comp;
@ -331,6 +330,7 @@ int VP8LHashChainFill(VP8LHashChain* const p, int quality,
int iter = iter_max;
int best_length = 0;
uint32_t best_distance = 0;
uint32_t best_argb;
const int min_pos =
(base_position > window_size) ? base_position - window_size : 0;
const int length_max = (max_len < 256) ? max_len : 256;
@ -360,26 +360,21 @@ int VP8LHashChainFill(VP8LHashChain* const p, int quality,
// Skip the for loop if we already have the maximum.
if (best_length == MAX_LENGTH) pos = min_pos - 1;
}
best_argb = argb_start[best_length];
for (; pos >= min_pos; pos = chain[pos]) {
for (; pos >= min_pos && --iter; pos = chain[pos]) {
int curr_length;
if (--iter < 0) {
break;
}
assert(base_position > (uint32_t)pos);
curr_length =
FindMatchLength(argb + pos, argb_start, best_length, max_len);
if (argb[pos + best_length] != best_argb) continue;
curr_length = VP8LVectorMismatch(argb + pos, argb_start, max_len);
if (best_length < curr_length) {
best_length = curr_length;
best_distance = base_position - pos;
// Stop if we have reached the maximum length. Otherwise, make sure
// we have executed a minimum number of iterations depending on the
// quality.
if ((best_length == MAX_LENGTH) ||
(curr_length >= length_max && iter < iter_min)) {
break;
}
best_argb = argb_start[best_length];
// Stop if we have reached a good enough length.
if (best_length >= length_max) break;
}
}
// We have the best match but in case the two intervals continue matching