PeerStreamer

/*

 * 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);

        }

    }

}