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faster, simpler and more accurate l3_unscale()

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Originally committed as revision 3924 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Michael Niedermayer 2005-02-01 23:43:07 +00:00
parent 711ae726f7
commit d04728bb57
1 changed files with 15 additions and 55 deletions
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70
libavcodec/mpegaudiodec.c
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@ -162,13 +162,9 @@ static VLC huff_quad_vlc[2];
/* computed from band_size_long */
static uint16_t band_index_long[9][23];
/* XXX: free when all decoders are closed */
#define TABLE_4_3_SIZE (8191 + 16)
#define TABLE_4_3_SIZE (8191 + 16)*4
static int8_t *table_4_3_exp;
#if FRAC_BITS <= 15
static uint16_t *table_4_3_value;
#else
static uint32_t *table_4_3_value;
#endif
/* intensity stereo coef table */
static int32_t is_table[2][16];
static int32_t is_table_lsf[2][2][16];
@ -191,14 +187,6 @@ static int32_t scale_factor_mult2[3][3] = {
SCALE_GEN(4.0 / 9.0), /* 9 steps */
};
/* 2^(n/4) */
static uint32_t scale_factor_mult3[4] = {
FIXR(1.0),
FIXR(1.18920711500272106671),
FIXR(1.41421356237309504880),
FIXR(1.68179283050742908605),
};
void ff_mpa_synth_init(MPA_INT *window);
static MPA_INT window[512] __attribute__((aligned(16)));
@ -236,32 +224,19 @@ static inline int l2_unscale_group(int steps, int mant, int scale_factor)
/* compute value^(4/3) * 2^(exponent/4). It normalized to FRAC_BITS */
static inline int l3_unscale(int value, int exponent)
{
#if FRAC_BITS <= 15
unsigned int m;
#else
uint64_t m;
#endif
int e;
e = table_4_3_exp[value];
e += (exponent >> 2);
e = FRAC_BITS - e;
#if FRAC_BITS <= 15
e = table_4_3_exp [4*value + (exponent&3)];
m = table_4_3_value[4*value + (exponent&3)];
e -= (exponent >> 2);
assert(e>=1);
if (e > 31)
#else
if (e > 63)
#endif
return 0;
m = table_4_3_value[value];
#if FRAC_BITS <= 15
m = (m * scale_factor_mult3[exponent & 3]);
m = (m + (1 << (e-1))) >> e;
return m;
#else
m = MUL64(m, scale_factor_mult3[exponent & 3]);
m = (m + (uint64_t_C(1) << (e-1))) >> e;
return m;
#endif
}
/* all integer n^(4/3) computation code */
@ -426,32 +401,17 @@ static int decode_init(AVCodecContext * avctx)
int_pow_init();
for(i=1;i<TABLE_4_3_SIZE;i++) {
int e, m;
m = int_pow(i, &e);
#if 0
/* test code */
{
double f, fm;
int e1, m1;
f = pow((double)i, 4.0 / 3.0);
fm = frexp(f, &e1);
m1 = FIXR(2 * fm);
#if FRAC_BITS <= 15
if ((unsigned short)m1 != m1) {
m1 = m1 >> 1;
e1++;
}
#endif
e1--;
if (m != m1 || e != e1) {
printf("%4d: m=%x m1=%x e=%d e1=%d\n",
i, m, m1, e, e1);
}
}
#endif
int e, m;
f = pow((double)(i/4), 4.0 / 3.0) * pow(2, (i&3)*0.25);
fm = frexp(f, &e);
m = FIXHR(fm*0.5);
e+= FRAC_BITS - 31;
/* normalized to FRAC_BITS */
table_4_3_value[i] = m;
table_4_3_exp[i] = e;
// av_log(NULL, AV_LOG_DEBUG, "%d %d %f\n", i, m, pow((double)i, 4.0 / 3.0));
table_4_3_exp[i] = -e;
}
for(i=0;i<7;i++) {