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/*
* fft.c
* Copyright 2011 John Lindgren
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions, and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions, and the following disclaimer in the documentation
* provided with the distribution.
*
* This software is provided "as is" and without any warranty, express or
* implied. In no event shall the authors be liable for any damages arising from
* the use of this software.
*/
// this version has few changes compared to the original audacious fft.c
// please find the original file in audacious
#ifdef HAVE_CONFIG_H
# include <config.h>
#endif
#include "deadbeef.h"
#include <math.h>
#include <complex.h>
#define N (DDB_FREQ_BANDS * 2)
static float hamming[N]; /* hamming window, scaled to sum to 1 */
static int reversed[N]; /* bit-reversal table */
static float complex roots[N / 2]; /* N-th roots of unity */
static int generated = 0;
static float LOGN; /* log N (base 2) */
/* Reverse the order of the lowest LOGN bits in an integer. */
static int bit_reverse (int x)
{
int y = 0;
for (int n = LOGN; n --; )
{
y = (y << 1) | (x & 1);
x >>= 1;
}
return y;
}
#ifndef HAVE_LOG2
static inline float log2(float x) {return (float)log(x)/M_LN2;}
#endif
/* Generate lookup tables. */
static void generate_tables (void)
{
if (generated)
return;
LOGN = log2(N);
for (int n = 0; n < N; n ++)
hamming[n] = 1 - 0.85 * cosf (2 * M_PI * n / N);
for (int n = 0; n < N; n ++)
reversed[n] = bit_reverse (n);
for (int n = 0; n < N / 2; n ++)
roots[n] = cexpf (2 * M_PI * I * n / N);
generated = 1;
}
static void do_fft (float complex a[N])
{
int half = 1; /* (2^s)/2 */
int inv = N / 2; /* N/(2^s) */
/* loop through steps */
while (inv)
{
/* loop through groups */
for (int g = 0; g < N; g += half << 1)
{
/* loop through butterflies */
for (int b = 0, r = 0; b < half; b ++, r += inv)
{
float complex even = a[g + b];
float complex odd = roots[r] * a[g + half + b];
a[g + b] = even + odd;
a[g + half + b] = even - odd;
}
}
half <<= 1;
inv >>= 1;
}
}
void
calc_freq (float *data, float *freq) {
generate_tables ();
// fft code shamelessly stolen from audacious
// thanks, John
float complex a[N];
for (int n = 0; n < N; n ++) {
a[reversed[n]] = data[n] * hamming[n];
}
do_fft(a);
for (int n = 0; n < N / 2 - 1; n ++)
freq[n] = 2 * cabsf (a[1 + n]) / N;
freq[N / 2 - 1] = cabsf(a[N / 2]) / N;
}
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