/*
  * reference discrete cosine transform (double precision)
  * Copyright (C) 2009 Dylan Yudaken
  *
  * 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
  */
 
 /**

  * @file

  * reference discrete cosine transform (double precision)
  *
  * @author Dylan Yudaken (dyudaken at gmail)
  *
  * @note This file could be optimized a lot, but is for
  * reference and so readability is better.
  */
 
 #include "libavutil/mathematics.h"

 #include "dctref.h"
 

 static double coefficients[8 * 8];
 
 /**
  * Initialize the double precision discrete cosine transform
  * functions fdct & idct.
  */
 av_cold void ff_ref_dct_init(void)
 {
     unsigned int i, j;
 
     for (j = 0; j < 8; ++j) {
         coefficients[j] = sqrt(0.125);
         for (i = 8; i < 64; i += 8) {
             coefficients[i + j] = 0.5 * cos(i * (j + 0.5) * M_PI / 64.0);
         }
     }
 }
 
 /**
  * Transform 8x8 block of data with a double precision forward DCT <br>
  * This is a reference implementation.
  *
  * @param block pointer to 8x8 block of data to transform
  */
 void ff_ref_fdct(short *block)
 {
     /* implement the equation: block = coefficients * block * coefficients' */
 
     unsigned int i, j, k;
     double out[8 * 8];
 
     /* out = coefficients * block */
     for (i = 0; i < 64; i += 8) {
         for (j = 0; j < 8; ++j) {
             double tmp = 0;
             for (k = 0; k < 8; ++k) {
                 tmp += coefficients[i + k] * block[k * 8 + j];
             }
             out[i + j] = tmp * 8;
         }
     }
 
     /* block = out * (coefficients') */
     for (j = 0; j < 8; ++j) {
         for (i = 0; i < 64; i += 8) {
             double tmp = 0;
             for (k = 0; k < 8; ++k) {
                 tmp += out[i + k] * coefficients[j * 8 + k];
             }
             block[i + j] = floor(tmp + 0.499999999999);
         }
     }
 }
 
 /**
  * Transform 8x8 block of data with a double precision inverse DCT <br>
  * This is a reference implementation.
  *
  * @param block pointer to 8x8 block of data to transform
  */
 void ff_ref_idct(short *block)
 {
     /* implement the equation: block = (coefficients') * block * coefficients */
 
     unsigned int i, j, k;
     double out[8 * 8];
 
     /* out = block * coefficients */
     for (i = 0; i < 64; i += 8) {
         for (j = 0; j < 8; ++j) {
             double tmp = 0;
             for (k = 0; k < 8; ++k) {
                 tmp += block[i + k] * coefficients[k * 8 + j];
             }
             out[i + j] = tmp;
         }
     }
 
     /* block = (coefficients') * out */
     for (i = 0; i < 8; ++i) {
         for (j = 0; j < 8; ++j) {
             double tmp = 0;
             for (k = 0; k < 64; k += 8) {
                 tmp += coefficients[k + i] * out[k + j];
             }
             block[i * 8 + j] = floor(tmp + 0.5);
         }
     }
 }