/* * (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" 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; } /* 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 void ff_dct_end(DCTContext *s) { ff_rdft_end(&s->rdft); av_free(s->csc2); }