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lavc/cbrt_tablegen: speed up tablegen

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This exploits an approach based on the sieve of Eratosthenes, a popular
method for generating prime numbers.

Tables are identical to previous ones.

Tested with FATE with/without --enable-hardcoded-tables.

Sample benchmark (Haswell, GNU/Linux+gcc):
prev:
7860100 decicycles in cbrt_tableinit,       1 runs,      0 skips
7777490 decicycles in cbrt_tableinit,       2 runs,      0 skips
[...]
7582339 decicycles in cbrt_tableinit,     256 runs,      0 skips
7563556 decicycles in cbrt_tableinit,     512 runs,      0 skips

new:
2099480 decicycles in cbrt_tableinit,       1 runs,      0 skips
2044470 decicycles in cbrt_tableinit,       2 runs,      0 skips
[...]
1796544 decicycles in cbrt_tableinit,     256 runs,      0 skips
1791631 decicycles in cbrt_tableinit,     512 runs,      0 skips

Both small and large run count given as this is called once so small run
count may give a better picture, small numbers are fairly consistent,
and there is a consistent downward trend from small to large runs,
at which point it stabilizes to a new value.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>
This commit is contained in:
Ganesh Ajjanagadde 2016-01-11 17:09:44 -05:00
parent f6e1c96730
commit 07a11ebcab
1 changed files with 29 additions and 10 deletions
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39
libavcodec/cbrt_tablegen.h
View File

@ -26,12 +26,13 @@
#include <stdint.h>
#include <math.h>
#include "libavutil/attributes.h"
#include "libavutil/intfloat.h"
#include "libavcodec/aac_defines.h"
#if USE_FIXED
#define CBRT(x) lrint((x).f * 8192)
#define CBRT(x) lrint((x) * 8192)
#else
#define CBRT(x) x.i
#define CBRT(x) av_float2int((float)(x))
#endif
#if CONFIG_HARDCODED_TABLES
@ -47,16 +48,34 @@ static uint32_t cbrt_tab[1 << 13];
static av_cold void AAC_RENAME(cbrt_tableinit)(void)
{
static double cbrt_tab_dbl[1 << 13];
if (!cbrt_tab[(1<<13) - 1]) {
int i;
for (i = 0; i < 1<<13; i++) {
union {
float f;
uint32_t i;
} f;
f.f = cbrt(i) * i;
cbrt_tab[i] = CBRT(f);
int i, j, k;
double cbrt_val;
for (i = 1; i < 1<<13; i++)
cbrt_tab_dbl[i] = 1;
/* have to take care of non-squarefree numbers */
for (i = 2; i < 90; i++) {
if (cbrt_tab_dbl[i] == 1) {
cbrt_val = i * cbrt(i);
for (k = i; k < 1<<13; k *= i)
for (j = k; j < 1<<13; j += k)
cbrt_tab_dbl[j] *= cbrt_val;
}
}
for (i = 91; i <= 8191; i+= 2) {
if (cbrt_tab_dbl[i] == 1) {
cbrt_val = i * cbrt(i);
for (j = i; j < 1<<13; j += i)
cbrt_tab_dbl[j] *= cbrt_val;
}
}
for (i = 0; i < 1<<13; i++)
cbrt_tab[i] = CBRT(cbrt_tab_dbl[i]);
}
}
#endif /* CONFIG_HARDCODED_TABLES */