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/*
* MDCT/IMDCT transforms
* Copyright (c) 2002 Fabrice Bellard
*
* This file is part of FFmpeg.
*
* FFmpeg is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* FFmpeg is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with FFmpeg; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdlib.h>
#include <string.h>
#include "libavutil/common.h"
#include "libavutil/mathematics.h"
#include "fft.h"
/**
* @file
* MDCT/IMDCT transforms.
*/
// Generate a Kaiser-Bessel Derived Window.
#define BESSEL_I0_ITER 50 // default: 50 iterations of Bessel I0 approximation
av_cold void ff_kbd_window_init(float *window, float alpha, int n)
{
int i, j;
double sum = 0.0, bessel, tmp;
double local_window[FF_KBD_WINDOW_MAX];
double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);
assert(n <= FF_KBD_WINDOW_MAX);
for (i = 0; i < n; i++) {
tmp = i * (n - i) * alpha2;
bessel = 1.0;
for (j = BESSEL_I0_ITER; j > 0; j--)
bessel = bessel * tmp / (j * j) + 1;
sum += bessel;
local_window[i] = sum;
}
sum++;
for (i = 0; i < n; i++)
window[i] = sqrt(local_window[i] / sum);
}
#include "mdct_tablegen.h"
/**
* init MDCT or IMDCT computation.
*/
av_cold int ff_mdct_init(FFTContext *s, int nbits, int inverse, double scale)
{
int n, n4, i;
double alpha, theta;
int tstep;
memset(s, 0, sizeof(*s));
n = 1 << nbits;
s->mdct_bits = nbits;
s->mdct_size = n;
n4 = n >> 2;
s->permutation = FF_MDCT_PERM_NONE;
if (ff_fft_init(s, s->mdct_bits - 2, inverse) < 0)
goto fail;
s->tcos = av_malloc(n/2 * sizeof(FFTSample));
if (!s->tcos)
goto fail;
switch (s->permutation) {
case FF_MDCT_PERM_NONE:
s->tsin = s->tcos + n4;
tstep = 1;
break;
case FF_MDCT_PERM_INTERLEAVE:
s->tsin = s->tcos + 1;
tstep = 2;
break;
default:
goto fail;
}
theta = 1.0 / 8.0 + (scale < 0 ? n4 : 0);
scale = sqrt(fabs(scale));
for(i=0;i<n4;i++) {
alpha = 2 * M_PI * (i + theta) / n;
s->tcos[i*tstep] = -cos(alpha) * scale;
s->tsin[i*tstep] = -sin(alpha) * scale;
}
return 0;
fail:
ff_mdct_end(s);
return -1;
}
/* complex multiplication: p = a * b */
#define CMUL(pre, pim, are, aim, bre, bim) \
{\
FFTSample _are = (are);\
FFTSample _aim = (aim);\
FFTSample _bre = (bre);\
FFTSample _bim = (bim);\
(pre) = _are * _bre - _aim * _bim;\
(pim) = _are * _bim + _aim * _bre;\
}
/**
* Compute the middle half of the inverse MDCT of size N = 2^nbits,
* thus excluding the parts that can be derived by symmetry
* @param output N/2 samples
* @param input N/2 samples
*/
void ff_imdct_half_c(FFTContext *s, FFTSample *output, const FFTSample *input)
{
int k, n8, n4, n2, n, j;
const uint16_t *revtab = s->revtab;
const FFTSample *tcos = s->tcos;
const FFTSample *tsin = s->tsin;
const FFTSample *in1, *in2;
FFTComplex *z = (FFTComplex *)output;
n = 1 << s->mdct_bits;
n2 = n >> 1;
n4 = n >> 2;
n8 = n >> 3;
/* pre rotation */
in1 = input;
in2 = input + n2 - 1;
for(k = 0; k < n4; k++) {
j=revtab[k];
CMUL(z[j].re, z[j].im, *in2, *in1, tcos[k], tsin[k]);
in1 += 2;
in2 -= 2;
}
ff_fft_calc(s, z);
/* post rotation + reordering */
for(k = 0; k < n8; k++) {
FFTSample r0, i0, r1, i1;
CMUL(r0, i1, z[n8-k-1].im, z[n8-k-1].re, tsin[n8-k-1], tcos[n8-k-1]);
CMUL(r1, i0, z[n8+k ].im, z[n8+k ].re, tsin[n8+k ], tcos[n8+k ]);
z[n8-k-1].re = r0;
z[n8-k-1].im = i0;
z[n8+k ].re = r1;
z[n8+k ].im = i1;
}
}
/**
* Compute inverse MDCT of size N = 2^nbits
* @param output N samples
* @param input N/2 samples
*/
void ff_imdct_calc_c(FFTContext *s, FFTSample *output, const FFTSample *input)
{
int k;
int n = 1 << s->mdct_bits;
int n2 = n >> 1;
int n4 = n >> 2;
ff_imdct_half_c(s, output+n4, input);
for(k = 0; k < n4; k++) {
output[k] = -output[n2-k-1];
output[n-k-1] = output[n2+k];
}
}
/**
* Compute MDCT of size N = 2^nbits
* @param input N samples
* @param out N/2 samples
*/
void ff_mdct_calc_c(FFTContext *s, FFTSample *out, const FFTSample *input)
{
int i, j, n, n8, n4, n2, n3;
FFTSample re, im;
const uint16_t *revtab = s->revtab;
const FFTSample *tcos = s->tcos;
const FFTSample *tsin = s->tsin;
FFTComplex *x = (FFTComplex *)out;
n = 1 << s->mdct_bits;
n2 = n >> 1;
n4 = n >> 2;
n8 = n >> 3;
n3 = 3 * n4;
/* pre rotation */
for(i=0;i<n8;i++) {
re = -input[2*i+3*n4] - input[n3-1-2*i];
im = -input[n4+2*i] + input[n4-1-2*i];
j = revtab[i];
CMUL(x[j].re, x[j].im, re, im, -tcos[i], tsin[i]);
re = input[2*i] - input[n2-1-2*i];
im = -(input[n2+2*i] + input[n-1-2*i]);
j = revtab[n8 + i];
CMUL(x[j].re, x[j].im, re, im, -tcos[n8 + i], tsin[n8 + i]);
}
ff_fft_calc(s, x);
/* post rotation */
for(i=0;i<n8;i++) {
FFTSample r0, i0, r1, i1;
CMUL(i1, r0, x[n8-i-1].re, x[n8-i-1].im, -tsin[n8-i-1], -tcos[n8-i-1]);
CMUL(i0, r1, x[n8+i ].re, x[n8+i ].im, -tsin[n8+i ], -tcos[n8+i ]);
x[n8-i-1].re = r0;
x[n8-i-1].im = i0;
x[n8+i ].re = r1;
x[n8+i ].im = i1;
}
}
av_cold void ff_mdct_end(FFTContext *s)
{
av_freep(&s->tcos);
ff_fft_end(s);
}
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