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dca: factorize scaling in inverse ADPCM

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Based on a patch from Christophe Gisquet.

Unrolling of the m == 0 case avoids a possible use of the uninitilized
value sum when s->predictor_history is not set. I failed to find a
sample for it. It also reduced the cycle count from 220 to 150 on
sandy bridge, x86_64 linux, gcc 4.8.2 compared to his patch.
This commit is contained in:
Janne Grunau 2014-02-21 13:13:36 +01:00
parent 08e3ea60ff
commit 7686afd049
1 changed files with 19 additions and 8 deletions
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27
libavcodec/dcadec.c
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@ -1192,16 +1192,27 @@ static int dca_subsubframe(DCAContext *s, int base_channel, int block_index)
*/
if (s->prediction_mode[k][l]) {
int n;
for (m = 0; m < 8; m++) {
for (n = 1; n <= 4; n++)
if (s->predictor_history)
subband_samples[k][l][0] += (adpcm_vb[s->prediction_vq[k][l]][0] *
s->subband_samples_hist[k][l][3] +
adpcm_vb[s->prediction_vq[k][l]][1] *
s->subband_samples_hist[k][l][2] +
adpcm_vb[s->prediction_vq[k][l]][2] *
s->subband_samples_hist[k][l][1] +
adpcm_vb[s->prediction_vq[k][l]][3] *
s->subband_samples_hist[k][l][0]) *
(1.0f / 8192);
for (m = 1; m < 8; m++) {
float sum = adpcm_vb[s->prediction_vq[k][l]][0] *
subband_samples[k][l][m - 1];
for (n = 2; n <= 4; n++)
if (m >= n)
subband_samples[k][l][m] +=
(adpcm_vb[s->prediction_vq[k][l]][n - 1] *
subband_samples[k][l][m - n] / 8192);
sum += adpcm_vb[s->prediction_vq[k][l]][n - 1] *
subband_samples[k][l][m - n];
else if (s->predictor_history)
subband_samples[k][l][m] +=
(adpcm_vb[s->prediction_vq[k][l]][n - 1] *
s->subband_samples_hist[k][l][m - n + 4] / 8192);
sum += adpcm_vb[s->prediction_vq[k][l]][n - 1] *
s->subband_samples_hist[k][l][m - n + 4];
subband_samples[k][l][m] += sum * 1.0f / 8192;
}
}
}