REAPER/epoch_tracker/fft.cc

/*
Copyright 2015 Google Inc. All rights reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/
// Author: David Talkin (dtalkin@google.com)

#include "epoch_tracker/fft.h"

/* Construct a FFT to perform a DFT of size 2^power. */
FFT::FFT(int power) {
  makefttable(power);
}

FFT::~FFT() {
  delete [] fsine;
  delete [] fcosine;
}

/*-----------------------------------------------------------------------*/
/* z <- (10 * log10(x^2 + y^2))  for n elements */
bool FFT::flog_mag(float *x, float *y, float *z, int n) {
  float *xp, *yp, *zp, t1, t2, ssq;

  if (x && y && z && n) {
    for (xp = x + n, yp = y + n, zp = z + n; zp > z;) {
      t1 = *--xp;
      t2 = *--yp;
      ssq = (t1 * t1) + (t2 * t2);
      *--zp = (ssq > 0.0)? 10.0 * log10(ssq) : -200.0;
    }
    return true;
  } else {
    return false;
  }
}

/*-----------------------------------------------------------------------*/
float FFT::get_band_rms(float *x, float*y, int first_bin, int last_bin) {
  double sum = 0.0;
  for (int i = first_bin; i <= last_bin; ++i) {
    sum += (x[i] * x[i]) + (y[i] * y[i]);
  }
  return sqrt(sum / (last_bin - first_bin + 1));
}

/*-----------------------------------------------------------------------*/
int FFT::makefttable(int pow2) {
  int lmx, lm;
  float *c, *s;
  double scl, arg;

  fftSize = 1 << pow2;
  fft_ftablesize = lmx = fftSize/2;
  fsine = new float[lmx];
  fcosine = new float[lmx];
  scl = (M_PI * 2.0) / fftSize;
  for (s = fsine, c = fcosine, lm = 0; lm < lmx; ++lm) {
    arg = scl * lm;
    *s++ = sin(arg);
    *c++ = cos(arg);
  }
  kbase = (fft_ftablesize * 2) / fftSize;
  power2 = pow2;
  return(fft_ftablesize);
}

/*-----------------------------------------------------------------------*/
/* Compute the discrete Fourier transform of the 2**l complex sequence
 * in x (real) and y (imaginary).  The DFT is computed in place and the
 * Fourier coefficients are returned in x and y.
 */
void FFT::fft(float *x, float *y) {
  float c, s,  t1, t2;
  int j1, j2, li, lix, i;
  int lmx, lo, lixnp, lm, j, nv2, k = kbase, im, jm, l = power2;

  for (lmx = fftSize, lo = 0; lo < l; lo++, k *= 2) {
    lix = lmx;
    lmx /= 2;
    lixnp = fftSize - lix;
    for (i = 0, lm = 0; lm < lmx; lm++, i += k) {
      c = fcosine[i];
      s = fsine[i];
      for (li = lixnp + lm, j1 = lm, j2 = lm + lmx; j1 <= li;
            j1 += lix, j2 += lix) {
        t1 = x[j1] - x[j2];
        t2 = y[j1] - y[j2];
        x[j1] += x[j2];
        y[j1] += y[j2];
        x[j2] = (c * t1) + (s * t2);
        y[j2] = (c * t2) - (s * t1);
      }
    }
  }

  /* Now perform the bit reversal. */
  j = 1;
  nv2 = fftSize / 2;
  for (i = 1; i < fftSize; i++) {
    if (j < i) {
      jm = j - 1;
      im = i - 1;
      t1 = x[jm];
      t2 = y[jm];
      x[jm] = x[im];
      y[jm] = y[im];
      x[im] = t1;
      y[im] = t2;
    }
    k = nv2;
    while (j > k) {
      j -= k;
      k /= 2;
    }
    j += k;
  }
}

/*-----------------------------------------------------------------------*/
/* Compute the discrete inverse Fourier transform of the 2**l complex
 * sequence in x (real) and y (imaginary).  The DFT is computed in
 * place and the Fourier coefficients are returned in x and y.  Note
 * that this DOES NOT scale the result by the inverse FFT size.
 */
void FFT::ifft(float *x, float *y) {
  float c, s,  t1, t2;
  int j1, j2, li, lix, i;
  int lmx, lo, lixnp, lm, j, nv2, k = kbase, im, jm, l = power2;

  for (lmx = fftSize, lo = 0; lo < l; lo++, k *= 2) {
    lix = lmx;
    lmx /= 2;
    lixnp = fftSize - lix;
    for (i = 0, lm = 0; lm < lmx; lm++, i += k) {
      c = fcosine[i];
      s = -fsine[i];
      for (li = lixnp + lm, j1 = lm, j2 = lm + lmx; j1 <= li;
            j1 += lix, j2 += lix) {
        t1 = x[j1] - x[j2];
        t2 = y[j1] - y[j2];
        x[j1] += x[j2];
        y[j1] += y[j2];
        x[j2] = (c * t1) + (s * t2);
        y[j2] = (c * t2) - (s * t1);
      }
    }
  }

  /* Now perform the bit reversal. */
  j = 1;
  nv2 = fftSize / 2;
  for (i = 1; i < fftSize; i++) {
    if (j < i) {
      jm = j-1;
      im = i-1;
      t1 = x[jm];
      t2 = y[jm];
      x[jm] = x[im];
      y[jm] = y[im];
      x[im] = t1;
      y[im] = t2;
    }
    k = nv2;
    while (j > k) {
      j -= k;
      k /= 2;
    }
    j += k;
  }
}