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fixed incorrect global gain - slightly increased precision of n^(4/3) table 

Originally committed as revision 557 to svn://svn.ffmpeg.org/ffmpeg/trunk
This commit is contained in:
Fabrice Bellard 2002-05-21 21:07:47 +00:00
parent 777cc95fb4
commit 59d3e367a8
1 changed files with 15 additions and 13 deletions
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28
libavcodec/mpegaudiodec.c
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@ -279,12 +279,17 @@ static int int_pow(int i, int *exp_ptr)
a = a << 1;
eq--;
}
*exp_ptr = eq;
#if POW_FRAC_BITS == FRAC_BITS
return a;
#else
return (a + (1 << (POW_FRAC_BITS - FRAC_BITS - 1))) >> (POW_FRAC_BITS - FRAC_BITS);
/* now POW_FRAC_ONE <= a < 2 * POW_FRAC_ONE */
#if (POW_FRAC_BITS - 1) > FRAC_BITS
a = (a + (1 << (POW_FRAC_BITS - FRAC_BITS - 1))) >> (POW_FRAC_BITS - FRAC_BITS);
/* correct overflow */
if (a >= 2 * (1 << FRAC_BITS)) {
a = a >> 1;
eq++;
}
#endif
*exp_ptr = eq;
return a;
}
static int decode_init(AVCodecContext * avctx)
@ -388,10 +393,6 @@ static int decode_init(AVCodecContext * avctx)
for(i=1;i<TABLE_4_3_SIZE;i++) {
int e, m;
m = int_pow(i, &e);
#if FRAC_BITS <= 15
if ((unsigned short)m != m)
m = 65535;
#endif
#if 0
/* test code */
{
@ -401,8 +402,10 @@ static int decode_init(AVCodecContext * avctx)
fm = frexp(f, &e1);
m1 = FIXR(2 * fm);
#if FRAC_BITS <= 15
if ((unsigned short)m1 != m1)
m1 = 65535;
if ((unsigned short)m1 != m1) {
m1 = m1 >> 1;
e1++;
}
#endif
e1--;
if (m != m1 || e != e1) {
@ -413,9 +416,8 @@ static int decode_init(AVCodecContext * avctx)
#endif
/* normalized to FRAC_BITS */
table_4_3_value[i] = m;
table_4_3_exp[i] = e - 1;
table_4_3_exp[i] = e;
}
for(i=0;i<7;i++) {
float f;