mirror of
https://github.com/FFmpeg/FFmpeg.git
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141 lines
3.5 KiB
C
141 lines
3.5 KiB
C
/*
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* (I)DCT Transforms
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* Copyright (c) 2009 Peter Ross <pross@xvid.org>
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* Copyright (c) 2010 Alex Converse <alex.converse@gmail.com>
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* Copyright (c) 2010 Vitor Sessak
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*
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* This file is part of FFmpeg.
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*
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* FFmpeg is free software; you can redistribute it and/or
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* modify it under the terms of the GNU Lesser General Public
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* License as published by the Free Software Foundation; either
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* version 2.1 of the License, or (at your option) any later version.
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*
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* FFmpeg is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* Lesser General Public License for more details.
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*
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* You should have received a copy of the GNU Lesser General Public
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* License along with FFmpeg; if not, write to the Free Software
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* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/**
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* @file libavcodec/dct.c
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* (Inverse) Discrete Cosine Transforms. These are also known as the
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* type II and type III DCTs respectively.
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*/
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#include <math.h>
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#include "libavutil/mathematics.h"
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#include "fft.h"
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av_cold int ff_dct_init(DCTContext *s, int nbits, int inverse)
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{
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int n = 1 << nbits;
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int i;
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s->nbits = nbits;
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s->inverse = inverse;
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ff_init_ff_cos_tabs(nbits+2);
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s->costab = ff_cos_tabs[nbits+2];
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s->csc2 = av_malloc(n/2 * sizeof(FFTSample));
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if (ff_rdft_init(&s->rdft, nbits, inverse) < 0) {
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av_free(s->csc2);
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return -1;
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}
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for (i = 0; i < n/2; i++)
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s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1)));
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return 0;
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}
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/* sin((M_PI * x / (2*n)) */
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#define SIN(s,n,x) (s->costab[(n) - (x)])
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/* cos((M_PI * x / (2*n)) */
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#define COS(s,n,x) (s->costab[x])
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static void ff_dct_calc_c(DCTContext *ctx, FFTSample *data)
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{
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int n = 1 << ctx->nbits;
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int i;
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if (ctx->inverse) {
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float next = data[n - 1];
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float inv_n = 1.0f / n;
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for (i = n - 2; i >= 2; i -= 2) {
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float val1 = data[i ];
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float val2 = data[i - 1] - data[i + 1];
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float c = COS(ctx, n, i);
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float s = SIN(ctx, n, i);
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data[i ] = c * val1 + s * val2;
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data[i + 1] = s * val1 - c * val2;
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}
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data[1] = 2 * next;
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ff_rdft_calc(&ctx->rdft, data);
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for (i = 0; i < n / 2; i++) {
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float tmp1 = data[i ] * inv_n;
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float tmp2 = data[n - i - 1] * inv_n;
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float csc = ctx->csc2[i] * (tmp1 - tmp2);
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tmp1 += tmp2;
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data[i ] = tmp1 + csc;
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data[n - i - 1] = tmp1 - csc;
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}
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} else {
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float next;
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for (i=0; i < n/2; i++) {
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float tmp1 = data[i ];
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float tmp2 = data[n - i - 1];
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float s = SIN(ctx, n, 2*i + 1);
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s *= tmp1 - tmp2;
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tmp1 = (tmp1 + tmp2) * 0.5f;
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data[i ] = tmp1 + s;
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data[n-i-1] = tmp1 - s;
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}
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ff_rdft_calc(&ctx->rdft, data);
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next = data[1] * 0.5;
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data[1] *= -1;
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for (i = n - 2; i >= 0; i -= 2) {
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float inr = data[i ];
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float ini = data[i + 1];
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float c = COS(ctx, n, i);
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float s = SIN(ctx, n, i);
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data[i ] = c * inr + s * ini;
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data[i+1] = next;
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next += s * inr - c * ini;
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}
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}
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}
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void ff_dct_calc(DCTContext *s, FFTSample *data)
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{
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ff_dct_calc_c(s, data);
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}
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av_cold void ff_dct_end(DCTContext *s)
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{
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ff_rdft_end(&s->rdft);
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av_free(s->csc2);
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}
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