106 lines
1.9 KiB
C++
106 lines
1.9 KiB
C++
/* -----------------------------------------------------------------------------
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GSFramework
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Copyright 2001-2013 Emmanuel Julien. All Rights Reserved.
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----------------------------------------------------------------------------- */
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#include <cmath>
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#include "picture/pict.h"
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//------------------------------------------------------------------------------
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void FFT(int size, bool inverse, float *inReal, float *inIm, float *outReal, float *outIm)
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{
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// Calculate m = log_2(n).
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int m = 0, p = 1;
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for (; p < size; ++m)
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p *= 2;
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// Bit reversal.
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outReal[size - 1] = inReal[size - 1];
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outIm[size - 1] = inIm[size - 1];
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int j = 0;
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for (int i = 0; i < size - 1; ++i)
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{
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outReal[i] = inReal[j];
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outIm[i] = inIm[j];
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int k = size / 2;
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while (k <= j)
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{
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j -= k;
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k /= 2;
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}
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j += k;
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}
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// Calculate the FFT.
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float ca = -1.0, sa = 0.0;
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int l1 = 1, l2 = 1;
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for (int l = 0; l < m; ++l)
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{
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l1 = l2;
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l2 *= 2;
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float u1 = 1.0, u2 = 0.0;
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for(int j = 0; j < l1; j++)
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{
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for(int i = j; i < size; i += l2)
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{
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int i1 = i + l1;
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float t1 = u1 * outReal[i1] - u2 * outIm[i1],
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t2 = u1 * outIm[i1] + u2 * outReal[i1];
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outReal[i1] = outReal[i] - t1;
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outIm[i1] = outIm[i] - t2;
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outReal[i] += t1;
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outIm[i] += t2;
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}
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double z = u1 * ca - u2 * sa;
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u2 = u1 * sa + u2 * ca;
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u1 = (float)z;
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}
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sa = (float)sqrt((1.f - ca) / 2.f);
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if (!inverse)
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sa = -sa;
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ca = (float)sqrt((1.f + ca) / 2.f);
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}
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// Divide through n if it isn't the IDFT.
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if (!inverse)
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for (int i = 0; i < size; ++i)
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{
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outReal[i] /= size;
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outIm[i] /= size;
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}
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}
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void testFFT()
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{
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float inR[8], inI[8], outR[8], outI[8];
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for (int n = 0; n < 8; ++n)
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{
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inR[n] = 5;
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inI[n] = 2;
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}
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FFT(8, false, inR, inI, outR, outI);
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for (int n = 0; n < 8; ++n)
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{
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inR[n] = 0;
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inI[n] = 0;
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}
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FFT(8, true, outR, outI, inR, inI);
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}
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//------------------------------------------------------------------------------
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