int fft_init_fix(FFTContext_fix *s, int nbits, int inverse)
{
int i, j, m, n;
double alpha, c1, s1, s2;
s->nbits = nbits;
n = 1 << nbits;
s->exptab = malloc((n / 2) * sizeof(FFTComplex_fix));
if (!s->exptab)
goto fail;
s->revtab = malloc(n * sizeof(unsigned short));
if (!s->revtab)
goto fail;
s->inverse = inverse;
s2 = inverse ? 1.0 : -1.0;
if(inverse)
s->fft_calc = fft_calc_fix_inverse;
else
s->fft_calc = fft_calc_fix;
s->imdct_calc = imdct_calc_fix;
for(i=0;i<(n/2);i++) {
alpha = 2 * M_PI * (double)i / (double)n;
c1 = cos(alpha);
s1 = sin(alpha) * s2;
s->exptab[i].re = FFT_SAMPLE(c1);
s->exptab[i].im = FFT_SAMPLE(s1);
}
/* compute bit reverse table */
for(i=0;i<n;i++) {
m=0;
for(j=0;j<nbits;j++) {
m |= ((i >> j) & 1) << (nbits-j-1);
}
s->revtab[i]=m;
}
return 0;
fail:
free(&s->revtab);
free(&s->exptab);
return -1;
}
/**
* init MDCT or IMDCT computation.
*/
int mdct_init_fix(MDCTContext_fix *s, int nbits, int inverse)
{
int n, n4, i;
double alpha;
memset(s, 0, sizeof(*s));
n = 1 << nbits;//1<<6 = 64
s->nbits = nbits;//6
s->n = n;//64
n4 = n >> 2;//16
s->tcos = malloc(n4 * sizeof(FFTSample_fix));
if (!s->tcos)
goto fail;
s->tsin = malloc(n4 * sizeof(FFTSample_fix));
if (!s->tsin)
goto fail;
for(i=0; i<n4; i++) { //n4 = 16
alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
s->tcos[i] = -FFT_SAMPLE(cos(alpha));
s->tsin[i] = -FFT_SAMPLE(sin(alpha));
}
if(inverse) {
s->mdct_calc = imdct_calc_fix;
s->imdct_half = imdct_half_fix_c;
} else {
s->mdct_calc = mdct_calc_fix; //need mdct function
}
if (fft_init_fix(&s->fft, s->nbits - 2, inverse) < 0)
goto fail;
return 0;
fail:
free(s->tcos);
free(s->tsin);
return -1;
}
