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.
---
libavcodec/dcadec.c | 27 +++++++++++++++++++--------
1 file changed, 19 insertions(+), 8 deletions(-)
diff --git a/libavcodec/dcadec.c b/libavcodec/dcadec.c
index c251db8..5ede61d 100644
--- a/libavcodec/dcadec.c
+++ b/libavcodec/dcadec.c
@@ -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;
}
}
}
--
1.9.0
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