/*
  * 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 "dsputil.h"
 

 /**

  * @file libavcodec/mdct.c

  * 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[n];
    double alpha2 = (alpha * M_PI / n) * (alpha * M_PI / n);

    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);
 }
 

 DECLARE_ALIGNED(16, float, ff_sine_128 [ 128]);
 DECLARE_ALIGNED(16, float, ff_sine_256 [ 256]);
 DECLARE_ALIGNED(16, float, ff_sine_512 [ 512]);
 DECLARE_ALIGNED(16, float, ff_sine_1024[1024]);
 DECLARE_ALIGNED(16, float, ff_sine_2048[2048]);

 DECLARE_ALIGNED(16, float, ff_sine_4096[4096]);
 float *ff_sine_windows[6] = {
     ff_sine_128, ff_sine_256, ff_sine_512, ff_sine_1024, ff_sine_2048, ff_sine_4096

 };
 

 // Generate a sine window.

 av_cold void ff_sine_window_init(float *window, int n) {

     int i;
     for(i = 0; i < n; i++)

         window[i] = sinf((i + 0.5) * (M_PI / (2.0 * n)));

 }
 

 /**
  * init MDCT or IMDCT computation.

  */

 av_cold int ff_mdct_init(MDCTContext *s, int nbits, int inverse)

 {
     int n, n4, i;

     double alpha;

 
     memset(s, 0, sizeof(*s));
     n = 1 << nbits;
     s->nbits = nbits;
     s->n = n;
     n4 = n >> 2;

     s->tcos = av_malloc(n4 * sizeof(FFTSample));

     if (!s->tcos)
         goto fail;

     s->tsin = av_malloc(n4 * sizeof(FFTSample));

     if (!s->tsin)
         goto fail;
 
     for(i=0;i<n4;i++) {
         alpha = 2 * M_PI * (i + 1.0 / 8.0) / n;
         s->tcos[i] = -cos(alpha);
         s->tsin[i] = -sin(alpha);
     }

     if (ff_fft_init(&s->fft, s->nbits - 2, inverse) < 0)

         goto fail;
     return 0;
  fail:
     av_freep(&s->tcos);
     av_freep(&s->tsin);
     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(MDCTContext *s, FFTSample *output, const FFTSample *input)

 {

     int k, n8, n4, n2, n, j;

     const uint16_t *revtab = s->fft.revtab;
     const FFTSample *tcos = s->tcos;
     const FFTSample *tsin = s->tsin;
     const FFTSample *in1, *in2;

     FFTComplex *z = (FFTComplex *)output;

 
     n = 1 << s->nbits;
     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->fft, z);

 
     /* post rotation + reordering */

     output += n4;
     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(MDCTContext *s, FFTSample *output, const FFTSample *input)

 {

     int k;
     int n = 1 << s->nbits;
     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(MDCTContext *s, FFTSample *out, const FFTSample *input)

 {
     int i, j, n, n8, n4, n2, n3;

     FFTSample re, im;

     const uint16_t *revtab = s->fft.revtab;
     const FFTSample *tcos = s->tcos;
     const FFTSample *tsin = s->tsin;

     FFTComplex *x = (FFTComplex *)out;

 
     n = 1 << s->nbits;
     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->fft, 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(MDCTContext *s)

 {
     av_freep(&s->tcos);
     av_freep(&s->tsin);

     ff_fft_end(&s->fft);

 }