PeerStreamer

/*

 * (I)DCT Transforms

 * Copyright (c) 2009 Peter Ross <pross@xvid.org>

 * Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>

 * Copyright (c) 2010 Vitor Sessak

 *

 * 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 St, Fifth Floor, Boston, MA  02110-1301  USA

 */

/**

 * @file libavcodec/dct.c

 * (Inverse) Discrete Cosine Transforms. These are also known as the

 * type II and type III DCTs respectively.

 */

#include <math.h>

#include "libavutil/mathematics.h"

#include "fft.h"

/* sin((M_PI * x / (2*n)) */

#define SIN(s,n,x) (s->costab[(n) - (x)])

/* cos((M_PI * x / (2*n)) */

#define COS(s,n,x) (s->costab[x])

static void ff_dct_calc_c(DCTContext *ctx, FFTSample *data)

{

    int n = 1 << ctx->nbits;

    int i;

    if (ctx->inverse) {

        float next = data[n - 1];

        float inv_n = 1.0f / n;

        for (i = n - 2; i >= 2; i -= 2) {

            float val1 = data[i    ];

            float val2 = data[i - 1] - data[i + 1];

            float c = COS(ctx, n, i);

            float s = SIN(ctx, n, i);

            data[i    ] = c * val1 + s * val2;

            data[i + 1] = s * val1 - c * val2;

        }

        data[1] = 2 * next;

        ff_rdft_calc(&ctx->rdft, data);

        for (i = 0; i < n / 2; i++) {

            float tmp1 = data[i        ] * inv_n;

            float tmp2 = data[n - i - 1] * inv_n;

            float csc = ctx->csc2[i] * (tmp1 - tmp2);

            tmp1 += tmp2;

            data[i        ] = tmp1 + csc;

            data[n - i - 1] = tmp1 - csc;

        }

    } else {

        float next;

        for (i=0; i < n/2; i++) {

            float tmp1 = data[i        ];

            float tmp2 = data[n - i - 1];

            float s = SIN(ctx, n, 2*i + 1);

            s *= tmp1 - tmp2;

            tmp1 = (tmp1 + tmp2) * 0.5f;

            data[i    ] = tmp1 + s;

            data[n-i-1] = tmp1 - s;

        }

        ff_rdft_calc(&ctx->rdft, data);

        next = data[1] * 0.5;

        data[1] *= -1;

        for (i = n - 2; i >= 0; i -= 2) {

            float inr = data[i    ];

            float ini = data[i + 1];

            float c = COS(ctx, n, i);

            float s = SIN(ctx, n, i);

            data[i  ] = c * inr + s * ini;

            data[i+1] = next;

            next +=     s * inr - c * ini;

        }

    }

}

void ff_dct_calc(DCTContext *s, FFTSample *data)

{

    ff_dct_calc_c(s, data);

}

av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)

{

    int n = 1 << nbits;

    int i;

    s->nbits    = nbits;

    s->inverse  = inverse;

    ff_init_ff_cos_tabs(nbits+2);

    s->costab = ff_cos_tabs[nbits+2];

    s->csc2 = av_malloc(n/2 * sizeof(FFTSample));

    if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {

        av_free(s->csc2);

        return -1;

    }

    for (i = 0; i < n/2; i++)

        s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));

    return 0;

}

av_cold void ff_dct_end(DCTContext *s)

{

    ff_rdft_end(&s->rdft);

    av_free(s->csc2);

}