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| author | Vitor Sessak <vitor1001@gmail.com> | 2010-06-28 04:55:36 +0000 |
|---|---|---|
| committer | Vitor Sessak <vitor1001@gmail.com> | 2010-06-28 04:55:36 +0000 |
| commit | 186d02150eabe58e1ccab06919adf245d8f5df08 (patch) | |
| tree | 340418e2ada9e37dbaa01927cf74046339f2149d | |
| parent | a64fadf62b19551e73e8d049bf4bbeca35a04553 (diff) | |
Use lookup table to avoid division in mp2 decoder
Originally committed as revision 23840 to svn://svn.ffmpeg.org/ffmpeg/trunk
| -rw-r--r-- | libavcodec/mpegaudiodec.c | 35 |
1 files changed, 29 insertions, 6 deletions
diff --git a/libavcodec/mpegaudiodec.c b/libavcodec/mpegaudiodec.c index 9ee5b604e9..bf85633d11 100644 --- a/libavcodec/mpegaudiodec.c +++ b/libavcodec/mpegaudiodec.c @@ -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); - steps = ff_mpa_quant_steps[qindex]; + 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); |