On 8/1/20, Andreas Rheinhardt <andreas.rheinha...@gmail.com> wrote:
> Besides the obvious advantage of less code this also has a performance
> impact: For GCC 9 the time spent on one call to smka_decode_frame() for
> the sample from ticket #2425 decreased from 1693619 to 1498127
> decicycles. For Clang 9, it decreased from 1369089 to 1366465
> decicycles.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
> ---
> The numbers for GCC surprised me (as did the fact that GCC was so much
> worse than Clang).
>
> libavcodec/smacker.c | 62 ++++++++++++++------------------------------
> 1 file changed, 20 insertions(+), 42 deletions(-)
>
> diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
> index d2b1c68162..ffd24c11e7 100644
> --- a/libavcodec/smacker.c
> +++ b/libavcodec/smacker.c
> @@ -671,37 +671,23 @@ static int smka_decode_frame(AVCodecContext *avctx,
> void *data,
> for(i = 0; i <= stereo; i++)
> *samples++ = pred[i];
> for(; i < unp_size / 2; i++) {
> + unsigned idx = 2 * (i & stereo);
> if (get_bits_left(&gb) < 0) {
> ret = AVERROR_INVALIDDATA;
> goto error;
> }
> - if(i & stereo) {
> - if(vlc[2].table)
> - res = get_vlc2(&gb, vlc[2].table, SMKTREE_BITS, 3);
> - else
> - res = values[2];
> - val = res;
> - if(vlc[3].table)
> - res = get_vlc2(&gb, vlc[3].table, SMKTREE_BITS, 3);
> - else
> - res = values[3];
> - val |= res << 8;
> - pred[1] += val;
> - *samples++ = pred[1];
> - } else {
> - if(vlc[0].table)
> - res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
> - else
> - res = values[0];
> - val = res;
> - if(vlc[1].table)
> - res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
> - else
> - res = values[1];
> - val |= res << 8;
> - pred[0] += val;
> - *samples++ = pred[0];
> - }
> + if (vlc[idx].table)
> + res = get_vlc2(&gb, vlc[idx].table, SMKTREE_BITS, 3);
> + else
> + res = values[idx];
> + val = res;
> + if (vlc[++idx].table)
> + res = get_vlc2(&gb, vlc[idx].table, SMKTREE_BITS, 3);
> + else
> + res = values[idx];
> + val |= res << 8;
> + pred[idx / 2] += val;
> + *samples++ = pred[idx / 2];
> }
> } else { //8-bit data
> for(i = stereo; i >= 0; i--)
> @@ -709,25 +695,17 @@ static int smka_decode_frame(AVCodecContext *avctx,
> void *data,
> for(i = 0; i <= stereo; i++)
> *samples8++ = pred[i];
> for(; i < unp_size; i++) {
> + unsigned idx = i & stereo;
> if (get_bits_left(&gb) < 0) {
> ret = AVERROR_INVALIDDATA;
> goto error;
> }
> - if(i & stereo){
> - if(vlc[1].table)
> - res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
> - else
> - res = values[1];
> - pred[1] += res;
> - *samples8++ = pred[1];
> - } else {
> - if(vlc[0].table)
> - res = get_vlc2(&gb, vlc[0].table, SMKTREE_BITS, 3);
> - else
> - res = values[0];
> - pred[0] += res;
> - *samples8++ = pred[0];
> - }
> + if (vlc[idx].table)
> + val = get_vlc2(&gb, vlc[idx].table, SMKTREE_BITS, 3);
> + else
> + val = values[idx];
> + pred[idx] += val;
> + *samples8++ = pred[idx];
> }
> }
>
> --
> 2.20.1
>
LGTM
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