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Speed up HashChainFindCopy function.

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Speed up HashChainFindCopy by optimizing on number of calls to
FindMatchLength method.
This change speeds up the lossless & lossy (Alpha) encoding by 20%
without loss of compression density.
At method=3, lossy (Alpha) compression speed (and density) remains
unchanged, as at that settings, the costly Backward Refs method is not
called

Change-Id: Ia1797148e9e4ee2787011837fa248afbae2242cb
This commit is contained in:
Vikas Arora 2013-07-16 19:56:37 -07:00
parent 6674014077
commit 7d60bbc6d9
1 changed files with 28 additions and 28 deletions
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56
src/enc/backward_references.c
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@ -163,7 +163,7 @@ static void GetParamsForHashChainFindCopy(int quality, int xsize,
static int HashChainFindCopy(const HashChain* const p,
int base_position, int xsize_signed,
const uint32_t* const argb, int maxlen,
const uint32_t* const argb, int max_len,
int window_size, int iter_pos, int iter_limit,
int* const distance_ptr,
int* const length_ptr) {
@ -176,25 +176,34 @@ static int HashChainFindCopy(const HashChain* const p,
(base_position > window_size) ? base_position - window_size : 0;
int pos;
assert(xsize > 0);
if (max_len > MAX_LENGTH) {
max_len = MAX_LENGTH;
}
for (pos = p->hash_to_first_index_[GetPixPairHash64(argb_start)];
pos >= min_pos;
pos = p->chain_[pos]) {
uint64_t val;
uint32_t curr_length;
uint32_t distance;
const uint64_t* const ptr1 =
(const uint64_t*)(argb + pos + best_length - 1);
const uint64_t* const ptr2 =
(const uint64_t*)(argb_start + best_length - 1);
if (iter_pos < 0) {
if (iter_pos < iter_limit || best_val >= 0xff0000) {
break;
}
}
--iter_pos;
if (argb[pos + best_length - 1] != argb_start[best_length - 1]) {
continue;
}
curr_length = FindMatchLength(argb + pos, argb_start, maxlen);
if (curr_length < best_length) {
continue;
}
// Before 'expensive' linear match, check if the two arrays match at the
// current best length index and also for the succeeding elements.
if (*ptr1 != *ptr2) continue;
curr_length = FindMatchLength(argb + pos, argb_start, max_len);
if (curr_length < best_length) continue;
distance = (uint32_t)(base_position - pos);
val = curr_length << 16;
// Favoring 2d locality here gives savings for certain images.
@ -213,7 +222,7 @@ static int HashChainFindCopy(const HashChain* const p,
best_val = val;
best_length = curr_length;
best_distance = distance;
if (curr_length >= MAX_LENGTH) {
if (curr_length >= (uint32_t)max_len) {
break;
}
if ((best_distance == 1 || distance == xsize) &&
@ -291,11 +300,8 @@ static int BackwardReferencesHashChain(int xsize, int ysize,
int offset = 0;
int len = 0;
if (i < pix_count - 1) { // FindCopy(i,..) reads pixels at [i] and [i + 1].
int maxlen = pix_count - i;
if (maxlen > MAX_LENGTH) {
maxlen = MAX_LENGTH;
}
HashChainFindCopy(hash_chain, i, xsize, argb, maxlen,
int max_len = pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset, &len);
}
@ -307,11 +313,8 @@ static int BackwardReferencesHashChain(int xsize, int ysize,
int k;
HashChainInsert(hash_chain, &argb[i], i);
if (i < pix_count - 2) { // FindCopy(i+1,..) reads [i + 1] and [i + 2].
int maxlen = pix_count - (i + 1);
if (maxlen > MAX_LENGTH) {
maxlen = MAX_LENGTH;
}
HashChainFindCopy(hash_chain, i + 1, xsize, argb, maxlen,
int max_len = pix_count - (i + 1);
HashChainFindCopy(hash_chain, i + 1, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset2, &len2);
if (len2 > len + 1) {
@ -522,11 +525,8 @@ static int BackwardReferencesHashChainDistanceOnly(
int offset = 0;
int len = 0;
if (i < pix_count - 1) { // FindCopy reads pixels at [i] and [i + 1].
int maxlen = shortmax ? 2 : MAX_LENGTH;
if (maxlen > pix_count - i) {
maxlen = pix_count - i;
}
HashChainFindCopy(hash_chain, i, xsize, argb, maxlen,
int max_len = shortmax ? 2 : pix_count - i;
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset, &len);
}
@ -650,12 +650,12 @@ static int BackwardReferencesHashChainFollowChosenPath(
for (ix = 0; ix < chosen_path_size; ++ix, ++size) {
int offset = 0;
int len = 0;
int maxlen = chosen_path[ix];
if (maxlen != 1) {
HashChainFindCopy(hash_chain, i, xsize, argb, maxlen,
int max_len = chosen_path[ix];
if (max_len != 1) {
HashChainFindCopy(hash_chain, i, xsize, argb, max_len,
window_size, iter_pos, iter_limit,
&offset, &len);
assert(len == maxlen);
assert(len == max_len);
refs->refs[size] = PixOrCopyCreateCopy(offset, len);
if (use_color_cache) {
for (k = 0; k < len; ++k) {