On 8/1/20, Andreas Rheinhardt <andreas.rheinha...@gmail.com> wrote:
> Up until now, the Smacker decoder has pretended that the prediction
> values are signed in code like 'pred[0] += (unsigned)sign_extend(val, 16)'
> (the cast has been added to this code later to fix undefined behaviour).
> This has been even done in case the PCM format is u8.
>
> Yet in case of 8/16 bit samples, only the lower 8/16 bit of the predicition
> values are ever used, so one can just as well just use unsigned and
> remove the sign extensions. This is what this commit does.
>
> For GCC 9 the time for one call to smka_decode_frame() for the sample from
> ticket #2425 decreased from 1709043 to 1693619 decicycles; for Clang 9
> it went up from 1355273 to 1369089 decicycles.
>
> Signed-off-by: Andreas Rheinhardt <andreas.rheinha...@gmail.com>
> ---
Should be fine if this code is completely covered by fate and thus
checksum are not changed.
> libavcodec/smacker.c | 13 ++++++-------
> 1 file changed, 6 insertions(+), 7 deletions(-)
>
> diff --git a/libavcodec/smacker.c b/libavcodec/smacker.c
> index e588b03820..d2b1c68162 100644
> --- a/libavcodec/smacker.c
> +++ b/libavcodec/smacker.c
> @@ -595,11 +595,10 @@ static int smka_decode_frame(AVCodecContext *avctx,
> void *data,
> int16_t *samples;
> uint8_t *samples8;
> uint8_t values[4];
> - int val;
> int i, res, ret;
> int unp_size;
> int bits, stereo;
> - int pred[2] = {0, 0};
> + unsigned pred[2], val;
>
> if (buf_size <= 4) {
> av_log(avctx, AV_LOG_ERROR, "packet is too small\n");
> @@ -668,7 +667,7 @@ static int smka_decode_frame(AVCodecContext *avctx, void
> *data,
> /* this codec relies on wraparound instead of clipping audio */
> if(bits) { //decode 16-bit data
> for(i = stereo; i >= 0; i--)
> - pred[i] = sign_extend(av_bswap16(get_bits(&gb, 16)), 16);
> + pred[i] = av_bswap16(get_bits(&gb, 16));
> for(i = 0; i <= stereo; i++)
> *samples++ = pred[i];
> for(; i < unp_size / 2; i++) {
> @@ -687,7 +686,7 @@ static int smka_decode_frame(AVCodecContext *avctx, void
> *data,
> else
> res = values[3];
> val |= res << 8;
> - pred[1] += (unsigned)sign_extend(val, 16);
> + pred[1] += val;
> *samples++ = pred[1];
> } else {
> if(vlc[0].table)
> @@ -700,7 +699,7 @@ static int smka_decode_frame(AVCodecContext *avctx, void
> *data,
> else
> res = values[1];
> val |= res << 8;
> - pred[0] += (unsigned)sign_extend(val, 16);
> + pred[0] += val;
> *samples++ = pred[0];
> }
> }
> @@ -719,14 +718,14 @@ static int smka_decode_frame(AVCodecContext *avctx,
> void *data,
> res = get_vlc2(&gb, vlc[1].table, SMKTREE_BITS, 3);
> else
> res = values[1];
> - pred[1] += sign_extend(res, 8);
> + 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] += sign_extend(res, 8);
> + pred[0] += res;
> *samples8++ = pred[0];
> }
> }
> --
> 2.20.1
>
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