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