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#include "config.h"
#include "alcomplex.h"
#include <math.h>
extern inline ALcomplex complex_add(ALcomplex a, ALcomplex b);
extern inline ALcomplex complex_sub(ALcomplex a, ALcomplex b);
extern inline ALcomplex complex_mult(ALcomplex a, ALcomplex b);
void complex_fft(ALcomplex *FFTBuffer, ALsizei FFTSize, ALdouble Sign)
{
ALsizei i, j, k, mask, step, step2;
ALcomplex temp, u, w;
ALdouble arg;
/* Bit-reversal permutation applied to a sequence of FFTSize items */
for(i = 1;i < FFTSize-1;i++)
{
for(mask = 0x1, j = 0;mask < FFTSize;mask <<= 1)
{
if((i&mask) != 0)
j++;
j <<= 1;
}
j >>= 1;
if(i < j)
{
temp = FFTBuffer[i];
FFTBuffer[i] = FFTBuffer[j];
FFTBuffer[j] = temp;
}
}
/* Iterative form of DanielsonLanczos lemma */
for(i = 1, step = 2;i < FFTSize;i<<=1, step<<=1)
{
step2 = step >> 1;
arg = M_PI / step2;
w.Real = cos(arg);
w.Imag = sin(arg) * Sign;
u.Real = 1.0;
u.Imag = 0.0;
for(j = 0;j < step2;j++)
{
for(k = j;k < FFTSize;k+=step)
{
temp = complex_mult(FFTBuffer[k+step2], u);
FFTBuffer[k+step2] = complex_sub(FFTBuffer[k], temp);
FFTBuffer[k] = complex_add(FFTBuffer[k], temp);
}
u = complex_mult(u, w);
}
}
}
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