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avcodec/smacker: Use unsigned for prediction values 

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.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
This commit is contained in:
Andreas Rheinhardt 2020-06-26 11:36:57 +02:00
parent 010e345afe
commit b2c42f0233
1 changed files with 6 additions and 7 deletions
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13
libavcodec/smacker.c
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@ -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];
}
}