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Use lookup table to avoid division in mp2 decoder

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Originally committed as revision 23840 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Vitor Sessak 2010-06-28 04:55:36 +00:00
parent a64fadf62b
commit 186d02150e
1 changed files with 29 additions and 6 deletions
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33
libavcodec/mpegaudiodec.c
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@ -97,6 +97,14 @@ static int32_t csa_table[8][4];
static float csa_table_float[8][4];
static INTFLOAT mdct_win[8][36];
static int16_t division_tab3[1<<6 ];
static int16_t division_tab5[1<<8 ];
static int16_t division_tab9[1<<11];
static int16_t * const division_tabs[4] = {
division_tab3, division_tab5, NULL, division_tab9
};
/* lower 2 bits: modulo 3, higher bits: shift */
static uint16_t scale_factor_modshift[64];
/* [i][j]: 2^(-j/3) * FRAC_ONE * 2^(i+2) / (2^(i+2) - 1) */
@ -399,6 +407,20 @@ static av_cold int decode_init(AVCodecContext * avctx)
int_pow_init();
mpegaudio_tableinit();
for (i = 0; i < 4; i++)
if (ff_mpa_quant_bits[i] < 0)
for (j = 0; j < (1<<(-ff_mpa_quant_bits[i]+1)); j++) {
int val1, val2, val3, steps;
int val = j;
steps = ff_mpa_quant_steps[i];
val1 = val % steps;
val /= steps;
val2 = val % steps;
val3 = val / steps;
division_tabs[i][j] = val1 + (val2 << 4) + (val3 << 8);
}
for(i=0;i<7;i++) {
float f;
INTFLOAT v;
@ -1268,17 +1290,18 @@ static int mp_decode_layer2(MPADecodeContext *s)
qindex = alloc_table[j+b];
bits = ff_mpa_quant_bits[qindex];
if (bits < 0) {
int v2;
/* 3 values at the same time */
v = get_bits(&s->gb, -bits);
v2 = division_tabs[qindex][v];
steps = ff_mpa_quant_steps[qindex];
s->sb_samples[ch][k * 12 + l + 0][i] =
l2_unscale_group(steps, v % steps, scale);
v = v / steps;
l2_unscale_group(steps, v2 & 15, scale);
s->sb_samples[ch][k * 12 + l + 1][i] =
l2_unscale_group(steps, v % steps, scale);
v = v / steps;
l2_unscale_group(steps, (v2 >> 4) & 15, scale);
s->sb_samples[ch][k * 12 + l + 2][i] =
l2_unscale_group(steps, v, scale);
l2_unscale_group(steps, v2 >> 8 , scale);
} else {
for(m=0;m<3;m++) {
v = get_bits(&s->gb, bits);