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/*
* 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 libavcodec/dctref.c
* 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);
}
}
}
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