[FFmpeg-devel] [PATCHv2] lavc/cbrt_tablegen: speed up tablegen

[Michael Niedermayer]

On Mon, Jan 04, 2016 at 06:33:59PM -0800, Ganesh Ajjanagadde wrote:
> 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.
> 
> Signed-off-by: Ganesh Ajjanagadde <gajjanagadde at gmail.com>
> ---
>  libavcodec/aacdec_fixed.c           |  4 +--
>  libavcodec/aacdec_template.c        |  2 +-
>  libavcodec/cbrt_tablegen.h          | 53 ++++++++++++++++++++++++++-----------
>  libavcodec/cbrt_tablegen_template.c | 12 ++++++++-
>  4 files changed, 51 insertions(+), 20 deletions(-)
> 
> diff --git a/libavcodec/aacdec_fixed.c b/libavcodec/aacdec_fixed.c
> index 396a874..f7b882b 100644
> --- a/libavcodec/aacdec_fixed.c
> +++ b/libavcodec/aacdec_fixed.c
> @@ -155,9 +155,9 @@ static void vector_pow43(int *coefs, int len)
>      for (i=0; i<len; i++) {
>          coef = coefs[i];
>          if (coef < 0)
> -            coef = -(int)cbrt_tab[-coef];
> +            coef = -(int)cbrt_tab[-coef].i;
>          else
> -            coef = (int)cbrt_tab[coef];
> +            coef = (int)cbrt_tab[coef].i;
>          coefs[i] = coef;
>      }
>  }
> diff --git a/libavcodec/aacdec_template.c b/libavcodec/aacdec_template.c
> index d819958..1380510 100644
> --- a/libavcodec/aacdec_template.c
> +++ b/libavcodec/aacdec_template.c
> @@ -1791,7 +1791,7 @@ static int decode_spectrum_and_dequant(AACContext *ac, INTFLOAT coef[1024],
>                                          v = -v;
>                                      *icf++ = v;
>  #else
> -                                    *icf++ = cbrt_tab[n] | (bits & 1U<<31);
> +                                    *icf++ = cbrt_tab[n].i | (bits & 1U<<31);
>  #endif /* USE_FIXED */
>                                      bits <<= 1;
>                                  } else {
> diff --git a/libavcodec/cbrt_tablegen.h b/libavcodec/cbrt_tablegen.h
> index 59b5a1d..e3d6634 100644
> --- a/libavcodec/cbrt_tablegen.h
> +++ b/libavcodec/cbrt_tablegen.h
> @@ -26,14 +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)
> -#else
> -#define CBRT(x) x.i
> -#endif
> -

> +union ff_int32float64 {
> +    uint32_t i;
> +    double   f;
> +};
>  #if CONFIG_HARDCODED_TABLES
>  #if USE_FIXED
>  #define cbrt_tableinit_fixed()
> @@ -43,20 +42,42 @@
>  #include "libavcodec/cbrt_tables.h"
>  #endif
>  #else
> -static uint32_t cbrt_tab[1 << 13];
> +static union ff_int32float64 cbrt_tab[1 << 13];

this doubles the size of the cpu cache needed at runtime to store
the same number of elements

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

it is not once nor twice but times without number that the same ideas make
their appearance in the world. -- Aristotle
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 181 bytes
Desc: Digital signature
URL: <http://ffmpeg.org/pipermail/ffmpeg-devel/attachments/20160108/c2ae4772/attachment.sig>