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WMA: use a table instead of pow() in decode_exp_vlc 

Originally committed as revision 20076 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Måns Rullgård 2009-09-29 10:38:27 +00:00
parent 4b4ac5c7a8
commit c0d1463da7
1 changed files with 73 additions and 4 deletions
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77
libavcodec/wmadec.c
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@ -240,6 +240,74 @@ static void decode_exp_lsp(WMACodecContext *s, int ch)
s->block_len, lsp_coefs);
}
/** pow(10, i / 16.0) for i in -60..67 */
static const float pow_tab[128] = {
1.7782794100389e-04, 2.0535250264571e-04,
2.3713737056617e-04, 2.7384196342644e-04,
3.1622776601684e-04, 3.6517412725484e-04,
4.2169650342858e-04, 4.8696752516586e-04,
5.6234132519035e-04, 6.4938163157621e-04,
7.4989420933246e-04, 8.6596432336006e-04,
1.0000000000000e-03, 1.1547819846895e-03,
1.3335214321633e-03, 1.5399265260595e-03,
1.7782794100389e-03, 2.0535250264571e-03,
2.3713737056617e-03, 2.7384196342644e-03,
3.1622776601684e-03, 3.6517412725484e-03,
4.2169650342858e-03, 4.8696752516586e-03,
5.6234132519035e-03, 6.4938163157621e-03,
7.4989420933246e-03, 8.6596432336006e-03,
1.0000000000000e-02, 1.1547819846895e-02,
1.3335214321633e-02, 1.5399265260595e-02,
1.7782794100389e-02, 2.0535250264571e-02,
2.3713737056617e-02, 2.7384196342644e-02,
3.1622776601684e-02, 3.6517412725484e-02,
4.2169650342858e-02, 4.8696752516586e-02,
5.6234132519035e-02, 6.4938163157621e-02,
7.4989420933246e-02, 8.6596432336007e-02,
1.0000000000000e-01, 1.1547819846895e-01,
1.3335214321633e-01, 1.5399265260595e-01,
1.7782794100389e-01, 2.0535250264571e-01,
2.3713737056617e-01, 2.7384196342644e-01,
3.1622776601684e-01, 3.6517412725484e-01,
4.2169650342858e-01, 4.8696752516586e-01,
5.6234132519035e-01, 6.4938163157621e-01,
7.4989420933246e-01, 8.6596432336007e-01,
1.0000000000000e+00, 1.1547819846895e+00,
1.3335214321633e+00, 1.5399265260595e+00,
1.7782794100389e+00, 2.0535250264571e+00,
2.3713737056617e+00, 2.7384196342644e+00,
3.1622776601684e+00, 3.6517412725484e+00,
4.2169650342858e+00, 4.8696752516586e+00,
5.6234132519035e+00, 6.4938163157621e+00,
7.4989420933246e+00, 8.6596432336007e+00,
1.0000000000000e+01, 1.1547819846895e+01,
1.3335214321633e+01, 1.5399265260595e+01,
1.7782794100389e+01, 2.0535250264571e+01,
2.3713737056617e+01, 2.7384196342644e+01,
3.1622776601684e+01, 3.6517412725484e+01,
4.2169650342858e+01, 4.8696752516586e+01,
5.6234132519035e+01, 6.4938163157621e+01,
7.4989420933246e+01, 8.6596432336007e+01,
1.0000000000000e+02, 1.1547819846895e+02,
1.3335214321633e+02, 1.5399265260595e+02,
1.7782794100389e+02, 2.0535250264571e+02,
2.3713737056617e+02, 2.7384196342644e+02,
3.1622776601684e+02, 3.6517412725484e+02,
4.2169650342858e+02, 4.8696752516586e+02,
5.6234132519035e+02, 6.4938163157621e+02,
7.4989420933246e+02, 8.6596432336007e+02,
1.0000000000000e+03, 1.1547819846895e+03,
1.3335214321633e+03, 1.5399265260595e+03,
1.7782794100389e+03, 2.0535250264571e+03,
2.3713737056617e+03, 2.7384196342644e+03,
3.1622776601684e+03, 3.6517412725484e+03,
4.2169650342858e+03, 4.8696752516586e+03,
5.6234132519035e+03, 6.4938163157621e+03,
7.4989420933246e+03, 8.6596432336007e+03,
1.0000000000000e+04, 1.1547819846895e+04,
1.3335214321633e+04, 1.5399265260595e+04,
};
/**
* decode exponents coded with VLC codes
*/
@ -248,6 +316,7 @@ static int decode_exp_vlc(WMACodecContext *s, int ch)
int last_exp, n, code;
const uint16_t *ptr;
float v, *q, max_scale, *q_end;
const float *ptab = pow_tab + 60;
ptr = s->exponent_bands[s->frame_len_bits - s->block_len_bits];
q = s->exponents[ch];
@ -255,8 +324,7 @@ static int decode_exp_vlc(WMACodecContext *s, int ch)
max_scale = 0;
if (s->version == 1) {
last_exp = get_bits(&s->gb, 5) + 10;
/* XXX: use a table */
v = pow(10, last_exp * (1.0 / 16.0));
v = ptab[last_exp];
max_scale = v;
n = *ptr++;
do {
@ -271,8 +339,9 @@ static int decode_exp_vlc(WMACodecContext *s, int ch)
return -1;
/* NOTE: this offset is the same as MPEG4 AAC ! */
last_exp += code - 60;
/* XXX: use a table */
v = pow(10, last_exp * (1.0 / 16.0));
if ((unsigned)last_exp + 60 > FF_ARRAY_ELEMS(pow_tab))
return -1;
v = ptab[last_exp];
if (v > max_scale)
max_scale = v;
n = *ptr++;