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avcodec/on2avc: Fix stability issues with scale_tab generation

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This also simplifies the code
the resulting values are binary identical to what pow(10, i/10.0) produces
This commit is contained in:
Michael Niedermayer 2015-12-27 10:55:48 +01:00
parent baf4c489e5
commit 3215342121
1 changed files with 7 additions and 33 deletions
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40
libavcodec/on2avc.c
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@ -912,23 +912,7 @@ static av_cold void on2avc_free_vlcs(On2AVCContext *c)
static av_cold int on2avc_decode_init(AVCodecContext *avctx)
{
On2AVCContext *c = avctx->priv_data;
int i, ph;
/* 10^(i*0.1) for 0 <= i < 10 */
/* TODO: possibly statically allocate scale_tab; this may help with FATE
* and reproducibility if the binary size is not impacted much */
static const double exp10_lut[] = {
1,
1.2589254117941673,
1.5848931924611136,
1.9952623149688795,
2.5118864315095806,
3.1622776601683795,
3.9810717055349727,
5.0118723362727229,
6.3095734448019334,
7.9432823472428158,
};
int64_t exp10_base = 10;
int i;
if (avctx->channels > 2U) {
avpriv_request_sample(avctx, "Decoding more than 2 channels");
@ -950,23 +934,13 @@ static av_cold int on2avc_decode_init(AVCodecContext *avctx)
av_log(avctx, AV_LOG_WARNING,
"Stereo mode support is not good, patch is welcome\n");
/* Fast and more accurate way of doing for (i = 0; i < 20; i++)
c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 16) / 32;
// We add -0.01 before ceil() to avoid any values to fall at exactly the
// midpoint between different ceil values. The results are identical to
// using pow(10, i / 10.0) without such bias
for (i = 0; i < 20; i++)
c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 16 - 0.01) / 32;
for (; i < 128; i++)
c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 0.5); */
for (i = 0; i < 10; i++) {
c->scale_tab[i] = ceil(exp10_lut[i] * 16) / 32;
c->scale_tab[i+10] = ceil(exp10_lut[i] * 160) / 32;
}
for (i = 20, ph = 0; i < 128; i++, ph++) {
if (i % 10 == 0) {
exp10_base *= 10;
ph = 0;
}
c->scale_tab[i] = ceil(exp10_base * exp10_lut[ph] * 0.5);
}
c->scale_tab[i] = ceil(ff_exp10(i * 0.1) * 0.5 - 0.01);
if (avctx->sample_rate < 32000 || avctx->channels == 1)
memcpy(c->long_win, ff_on2avc_window_long_24000,