ref: 0d1f2bd7bb45a4915cff6f4d1d5e6a8fafb8c26a
dir: /transfo.c/
#include <math.h>
#include "all.h"
#include "transfo.h"
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
#ifndef M_PI_2
#define M_PI_2 1.57079632679489661923
#endif
/*****************************
Fast MDCT & IMDCT Code
*****************************/
void MDCT (fftw_real *data, int N) {
fftw_real tempr, tempi, c, s, cold, cfreq, sfreq; /* temps for pre and post twiddle */
fftw_real freq = 2.0 * M_PI / N;
fftw_real fac,cosfreq8,sinfreq8;
int i, n;
int b = N >> 1;
int N4 = N >> 2;
int N2 = N >> 1;
int a = N - b;
int a2 = a >> 1;
int a4 = a >> 2;
int b4 = b >> 2;
int unscambled;
/* Choosing to allocate 2/N factor to Inverse Xform! */
fac = 2.; /* 2 from MDCT inverse to forward */
/* prepare for recurrence relation in pre-twiddle */
cfreq = cos (freq);
sfreq = sin (freq);
cosfreq8 = cos (freq * 0.125);
sinfreq8 = sin (freq * 0.125);
c = cosfreq8;
s = sinfreq8;
for (i = 0; i < N4; i++) {
/* calculate real and imaginary parts of g(n) or G(p) */
n = N / 2 - 1 - 2 * i;
if (i < b4) {
tempr = data [a2 + n] + data [N + a2 - 1 - n]; /* use second form of e(n) for n = N / 2 - 1 - 2i */
} else {
tempr = data [a2 + n] - data [a2 - 1 - n]; /* use first form of e(n) for n = N / 2 - 1 - 2i */
}
n = 2 * i;
if (i < a4) {
tempi = data [a2 + n] - data [a2 - 1 - n]; /* use first form of e(n) for n=2i */
} else {
tempi = data [a2 + n] + data [N + a2 - 1 - n]; /* use second form of e(n) for n=2i*/
}
/* calculate pre-twiddled FFT input */
FFTarray [i].re = tempr * c + tempi * s;
FFTarray [i].im = tempi * c - tempr * s;
/* use recurrence to prepare cosine and sine for next value of i */
cold = c;
c = c * cfreq - s * sfreq;
s = s * cfreq + cold * sfreq;
}
/* Perform in-place complex FFT of length N/4 */
switch (N) {
case 256: pfftw_64(FFTarray);
break;
case 2048:pfftw_512(FFTarray);
}
/* prepare for recurrence relations in post-twiddle */
c = cosfreq8;
s = sinfreq8;
/* post-twiddle FFT output and then get output data */
for (i = 0; i < N4; i++) {
/* get post-twiddled FFT output */
/* Note: fac allocates 4/N factor from IFFT to forward and inverse */
switch (N) {
case 256:
unscambled = unscambled64[i];
break;
case 2048:
unscambled = unscambled512[i];
}
tempr = fac * (FFTarray [unscambled].re * c + FFTarray [unscambled].im * s);
tempi = fac * (FFTarray [unscambled].im * c - FFTarray [unscambled].re * s);
/* fill in output values */
data [2 * i] = -tempr; /* first half even */
data [N2 - 1 - 2 * i] = tempi; /* first half odd */
data [N2 + 2 * i] = -tempi; /* second half even */
data [N - 1 - 2 * i] = tempr; /* second half odd */
/* use recurrence to prepare cosine and sine for next value of i */
cold = c;
c = c * cfreq - s * sfreq;
s = s * cfreq + cold * sfreq;
}
}
void IMDCT(fftw_real *data, int N)
{
fftw_real tempr, tempi, c, s, cold, cfreq, sfreq; /* temps for pre and post twiddle */
fftw_real freq = 2.0 * M_PI / N;
fftw_real fac, cosfreq8, sinfreq8;
int i;
int Nd2 = N >> 1;
int Nd4 = N >> 2;
int Nd8 = N >> 3;
int unscambled;
/* Choosing to allocate 2/N factor to Inverse Xform! */
fac = 2. / N; /* remaining 2/N from 4/N IFFT factor */
/* prepare for recurrence relation in pre-twiddle */
cfreq = cos (freq);
sfreq = sin (freq);
cosfreq8 = cos (freq * 0.125);
sinfreq8 = sin (freq * 0.125);
c = cosfreq8;
s = sinfreq8;
for (i = 0; i < Nd4; i++) {
/* calculate real and imaginary parts of g(n) or G(p) */
tempr = -data [2 * i];
tempi = data [Nd2 - 1 - 2 * i];
/* calculate pre-twiddled FFT input */
switch (N) {
case 256:
unscambled = unscambled64[i];
break;
case 2048:
unscambled = unscambled512[i];
}
FFTarray [unscambled].re = tempr * c - tempi * s;
FFTarray [unscambled].im = tempi * c + tempr * s;
/* use recurrence to prepare cosine and sine for next value of i */
cold = c;
c = c * cfreq - s * sfreq;
s = s * cfreq + cold * sfreq;
}
/* Perform in-place complex IFFT of length N/4 */
switch (N) {
case 256: pfftwi_64(FFTarray);
break;
case 2048:pfftwi_512(FFTarray);
}
/* prepare for recurrence relations in post-twiddle */
c = cosfreq8;
s = sinfreq8;
/* post-twiddle FFT output and then get output data */
for (i = 0; i < Nd4; i++) {
/* get post-twiddled FFT output */
tempr = fac * (FFTarray[i].re * c - FFTarray[i].im * s);
tempi = fac * (FFTarray[i].im * c + FFTarray[i].re * s);
/* fill in output values */
data [Nd2 + Nd4 - 1 - 2 * i] = tempr;
if (i < Nd8) {
data [Nd2 + Nd4 + 2 * i] = tempr;
} else {
data [2 * i - Nd4] = -tempr;
}
data [Nd4 + 2 * i] = tempi;
if (i < Nd8) {
data [Nd4 - 1 - 2 * i] = -tempi;
} else {
data [Nd4 + N - 1 - 2*i] = tempi;
}
/* use recurrence to prepare cosine and sine for next value of i */
cold = c;
c = c * cfreq - s * sfreq;
s = s * cfreq + cold * sfreq;
}
}