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Code Issues Releases Activity

mp3dec: adjust IMDCT scaling to avoid overflows

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Fixes ticket268

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer 2012-08-02 04:21:53 +02:00
parent 98a2f4e87b
commit 571572fcdd
3 changed files with 5 additions and 3 deletions
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2
libavcodec/mpegaudio.h
View File

@ -52,6 +52,8 @@
#define WFRAC_BITS 16 /* fractional bits for window */
#endif
#define IMDCT_SCALAR 1.759
#define FRAC_ONE (1 << FRAC_BITS)
#define FIX(a) ((int)((a) * FRAC_ONE))

4
libavcodec/mpegaudio_tablegen.h
View File

@ -47,7 +47,7 @@ static void mpegaudio_tableinit(void)
double value = i / 4;
double f, fm;
int e, m;
f = value * cbrtf(value) * pow(2, (i & 3) * 0.25);
f = value / IMDCT_SCALAR * cbrtf(value) * pow(2, (i & 3) * 0.25);
fm = frexp(f, &e);
m = (uint32_t)(fm * (1LL << 31) + 0.5);
e += FRAC_BITS - 31 + 5 - 100;
@ -58,7 +58,7 @@ static void mpegaudio_tableinit(void)
}
for (exponent = 0; exponent < 512; exponent++) {
for (value = 0; value < 16; value++) {
double f = (double)value * cbrtf(value) * pow(2, (exponent - 400) * 0.25 + FRAC_BITS + 5);
double f = (double)value * cbrtf(value) * pow(2, (exponent - 400) * 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR;
expval_table_fixed[exponent][value] = llrint(f);
expval_table_float[exponent][value] = f;
}

2
libavcodec/mpegaudiodsp_template.c
View File

@ -243,7 +243,7 @@ void RENAME(ff_init_mpadsp_tabs)(void)
else if (i < 18) d = 1;
}
//merge last stage of imdct into the window coefficients
d *= 0.5 / cos(M_PI * (2 * i + 19) / 72);
d *= 0.5 * IMDCT_SCALAR / cos(M_PI * (2 * i + 19) / 72);
if (j == 2)
RENAME(ff_mdct_win)[j][i/3] = FIXHR((d / (1<<5)));