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lavc/pcm_tablegen: slight speedup of table generation

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This gets rid of some branches to speed up table generation slightly
(impact higher on mulaw than alaw). Tables are identical to before,
tested with FATE.

Sample benchmark (Haswell, GNU/Linux+gcc):
old:
 313494 decicycles in build_alaw_table,    4094 runs,      2 skips
 315959 decicycles in build_alaw_table,    8190 runs,      2 skips

 323599 decicycles in build_ulaw_table,    4095 runs,      1 skips
 318849 decicycles in build_ulaw_table,    8188 runs,      4 skips

new:
 261902 decicycles in build_alaw_table,    4096 runs,      0 skips
 266519 decicycles in build_alaw_table,    8192 runs,      0 skips

 209657 decicycles in build_ulaw_table,    4096 runs,      0 skips
 232656 decicycles in build_ulaw_table,    8192 runs,      0 skips

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
This commit is contained in:
Ganesh Ajjanagadde 2015-12-30 20:02:11 -08:00
parent 7cc01c2572
commit 43624a669b
1 changed files with 12 additions and 12 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

24
libavcodec/pcm_tablegen.h
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@ -87,21 +87,21 @@ static av_cold void build_xlaw_table(uint8_t *linear_to_xlaw,
{
int i, j, v, v1, v2;
j = 0;
for(i=0;i<128;i++) {
if (i != 127) {
v1 = xlaw2linear(i ^ mask);
v2 = xlaw2linear((i + 1) ^ mask);
v = (v1 + v2 + 4) >> 3;
} else {
v = 8192;
}
for(;j<v;j++) {
j = 1;
linear_to_xlaw[8192] = mask;
for(i=0;i<127;i++) {
v1 = xlaw2linear(i ^ mask);
v2 = xlaw2linear((i + 1) ^ mask);
v = (v1 + v2 + 4) >> 3;
for(;j<v;j+=1) {
linear_to_xlaw[8192 - j] = (i ^ (mask ^ 0x80));
linear_to_xlaw[8192 + j] = (i ^ mask);
if (j > 0)
linear_to_xlaw[8192 - j] = (i ^ (mask ^ 0x80));
}
}
for(;j<8192;j++) {
linear_to_xlaw[8192 - j] = (127 ^ (mask ^ 0x80));
linear_to_xlaw[8192 + j] = (127 ^ mask);
}
linear_to_xlaw[0] = linear_to_xlaw[1];
}