[FFmpeg-devel] [PATCH] avcodec: use av_mod_intp2() where possible

[Michael Niedermayer]

On Tue, Apr 21, 2015 at 05:45:25PM -0300, James Almer wrote:
> Signed-off-by: James Almer <jamrial at gmail.com>
> ---
>  libavcodec/acelp_vectors.c     |  8 +++-----
>  libavcodec/adpcm.c             |  2 +-
>  libavcodec/alacenc.c           |  3 +--
>  libavcodec/atrac3plus.c        |  4 ++--
>  libavcodec/dnxhdenc.c          |  2 +-
>  libavcodec/dvenc.c             |  2 +-
>  libavcodec/ffv1.h              |  2 +-
>  libavcodec/ffv1dec.c           |  3 +--
>  libavcodec/g726.c              |  2 +-
>  libavcodec/g729dec.c           |  2 +-
>  libavcodec/golomb.h            |  2 +-
>  libavcodec/h264.c              |  5 ++---
>  libavcodec/h264_refs.c         |  2 +-
>  libavcodec/hevc.c              | 26 ++++++++++++--------------
>  libavcodec/hevc_cabac.c        |  8 ++++----
>  libavcodec/hevc_filter.c       | 15 ++++++---------
>  libavcodec/hevc_mvs.c          |  4 ++--
>  libavcodec/hevc_ps.c           |  4 ++--
>  libavcodec/hevc_refs.c         |  5 ++---
>  libavcodec/hevcpred_template.c |  4 ++--
>  libavcodec/mpeg12enc.c         |  8 ++++----
>  libavcodec/opus.h              |  2 +-
>  libavcodec/opus_celt.c         |  9 ++++-----
>  libavcodec/proresenc_kostya.c  |  6 ++----
>  libavcodec/put_bits.h          |  2 +-
>  libavcodec/vorbisdec.c         |  5 ++---
>  26 files changed, 61 insertions(+), 76 deletions(-)
> 
> diff --git a/libavcodec/acelp_vectors.c b/libavcodec/acelp_vectors.c
> index 86851a3..7aef8c7 100644
> --- a/libavcodec/acelp_vectors.c
> +++ b/libavcodec/acelp_vectors.c
> @@ -133,12 +133,11 @@ void ff_acelp_fc_pulse_per_track(
>          int pulse_count,
>          int bits)
>  {
> -    int mask = (1 << bits) - 1;
>      int i;
>  
>      for(i=0; i<pulse_count; i++)
>      {
> -        fc_v[i + tab1[pulse_indexes & mask]] +=
> +        fc_v[i + tab1[av_mod_uintp2(pulse_indexes, bits)]] +=
>                  (pulse_signs & 1) ? 8191 : -8192; // +/-1 in (2.13)
>  
>          pulse_indexes >>= bits;
> @@ -154,13 +153,12 @@ void ff_decode_10_pulses_35bits(const int16_t *fixed_index,
>                                  int half_pulse_count, int bits)
>  {
>      int i;
> -    int mask = (1 << bits) - 1;
>  
>      fixed_sparse->no_repeat_mask = 0;
>      fixed_sparse->n = 2 * half_pulse_count;
>      for (i = 0; i < half_pulse_count; i++) {
> -        const int pos1   = gray_decode[fixed_index[2*i+1] & mask] + i;
> -        const int pos2   = gray_decode[fixed_index[2*i  ] & mask] + i;
> +        const int pos1   = gray_decode[av_mod_uintp2(fixed_index[2*i+1], bits)] + i;
> +        const int pos2   = gray_decode[av_mod_uintp2(fixed_index[2*i  ], bits)] + i;
>          const float sign = (fixed_index[2*i+1] & (1 << bits)) ? -1.0 : 1.0;
>          fixed_sparse->x[2*i+1] = pos1;
>          fixed_sparse->x[2*i  ] = pos2;
[...]
> diff --git a/libavcodec/ffv1.h b/libavcodec/ffv1.h
> index 5081397..bfc4d71 100644
> --- a/libavcodec/ffv1.h
> +++ b/libavcodec/ffv1.h
> @@ -143,7 +143,7 @@ static av_always_inline int fold(int diff, int bits)
>          diff = (int8_t)diff;
>      else {
>          diff +=  1 << (bits  - 1);
> -        diff &= (1 <<  bits) - 1;
> +        diff  = av_mod_uintp2(diff, bits);
>          diff -=  1 << (bits  - 1);
>      }
>  

iam not sure some of these changes are are a good idea
for example above the mask has to be calculated anyway what can be
gained from av_mod_uintp2() use here ?
i think this should be bechmarked when its in performance critical code

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

Awnsering whenever a program halts or runs forever is
On a turing machine, in general impossible (turings halting problem).
On any real computer, always possible as a real computer has a finite number
of states N, and will either halt in less than N cycles or never halt.
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