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avcodec: improve precission for cbrtf() emulation

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cbrtf() took floats but it represented 1/3 exactly
and even if not more precission should be better in theory
for the table generation

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
This commit is contained in:
Michael Niedermayer
2013-10-15 20:06:44 +02:00
parent e516921143
commit 59352a07d8
2 changed files with 3 additions and 3 deletions
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2
libavcodec/cbrt_tablegen.h
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@@ -42,7 +42,7 @@ static void cbrt_tableinit(void)
float f;
uint32_t i;
} f;
f.f = powf(i, 1.0 / 3.0) * i;
f.f = pow(i, 1.0 / 3.0) * i;
cbrt_tab[i] = f.i;
}
}

4
libavcodec/mpegaudio_tablegen.h
View File

@@ -49,7 +49,7 @@ static void mpegaudio_tableinit(void)
double f, fm;
int e, m;
/* cbrtf() isn't available on all systems, so we use powf(). */
f = value / IMDCT_SCALAR * powf(value, 1.0 / 3.0) * pow(2, (i & 3) * 0.25);
f = value / IMDCT_SCALAR * pow(value, 1.0 / 3.0) * pow(2, (i & 3) * 0.25);
fm = frexp(f, &e);
m = (uint32_t)(fm * (1LL << 31) + 0.5);
e += FRAC_BITS - 31 + 5 - 100;
@@ -61,7 +61,7 @@ static void mpegaudio_tableinit(void)
for (exponent = 0; exponent < 512; exponent++) {
for (value = 0; value < 16; value++) {
/* cbrtf() isn't available on all systems, so we use powf(). */
double f = (double)value * powf(value, 1.0 / 3.0) * pow(2, (exponent - 400) * 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR;
double f = (double)value * pow(value, 1.0 / 3.0) * pow(2, (exponent - 400) * 0.25 + FRAC_BITS + 5) / IMDCT_SCALAR;
/* llrint() isn't always available, so round and cast manually. */
expval_table_fixed[exponent][value] = (long long int) (f >= 0 ? floor(f + 0.5) : ceil(f - 0.5));
expval_table_float[exponent][value] = f;