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change brute force search to min-heap. 3.6x faster generate_len_table, 8% faster ffvhuff encoding.

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Originally committed as revision 9069 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Loren Merritt 2007-05-19 02:32:59 +00:00
parent d2f43ca998
commit 98ef8c324c
1 changed files with 43 additions and 43 deletions
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86
libavcodec/huffyuv.c
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@ -261,57 +261,57 @@ static int generate_bits_table(uint32_t *dst, uint8_t *len_table){
}
#ifdef CONFIG_ENCODERS
typedef struct {
uint64_t val;
int name;
} heap_elem_t;
static void heap_sift(heap_elem_t *h, int root, int size)
{
while(root*2+1 < size) {
int child = root*2+1;
if(child < size-1 && h[child].val > h[child+1].val)
child++;
if(h[root].val > h[child].val) {
FFSWAP(heap_elem_t, h[root], h[child]);
root = child;
} else
break;
}
}
static void generate_len_table(uint8_t *dst, uint64_t *stats, int size){
uint64_t counts[2*size];
heap_elem_t h[size];
int up[2*size];
int len[2*size];
int offset, i, next;
for(offset=1; ; offset<<=1){
for(i=0; i<size; i++){
counts[i]= stats[i] + offset - 1;
h[i].name = i;
h[i].val = (stats[i] << 8) + offset;
}
for(i=size/2-1; i>=0; i--)
heap_sift(h, i, size);
for(next=size; next<size*2-1; next++){
// merge the two smallest entries, and put it back in the heap
uint64_t min1v = h[0].val;
up[h[0].name] = next;
h[0].val = INT64_MAX;
heap_sift(h, 0, size);
up[h[0].name] = next;
h[0].name = next;
h[0].val += min1v;
heap_sift(h, 0, size);
}
for(next=size; next<size*2; next++){
uint64_t min1, min2;
int min1_i, min2_i;
min1=min2= INT64_MAX;
min1_i= min2_i=-1;
for(i=0; i<next; i++){
if(min2 > counts[i]){
if(min1 > counts[i]){
min2= min1;
min2_i= min1_i;
min1= counts[i];
min1_i= i;
}else{
min2= counts[i];
min2_i= i;
}
}
}
if(min2==INT64_MAX) break;
counts[next]= min1 + min2;
counts[min1_i]=
counts[min2_i]= INT64_MAX;
up[min1_i]=
up[min2_i]= next;
up[next]= -1;
}
for(i=0; i<size; i++){
int len;
int index=i;
for(len=0; up[index] != -1; len++)
index= up[index];
if(len >= 32) break;
dst[i]= len;
len[2*size-2] = 0;
for(i=2*size-3; i>=size; i--)
len[i] = len[up[i]] + 1;
for(i=0; i<size; i++) {
dst[i] = len[up[i]] + 1;
if(dst[i] > 32) break;
}
if(i==size) break;
}