Libav
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00001 /* 00002 * (I)DCT Transforms 00003 * Copyright (c) 2009 Peter Ross <pross@xvid.org> 00004 * Copyright (c) 2010 Alex Converse <alex.converse@gmail.com> 00005 * Copyright (c) 2010 Vitor Sessak 00006 * 00007 * This file is part of FFmpeg. 00008 * 00009 * FFmpeg is free software; you can redistribute it and/or 00010 * modify it under the terms of the GNU Lesser General Public 00011 * License as published by the Free Software Foundation; either 00012 * version 2.1 of the License, or (at your option) any later version. 00013 * 00014 * FFmpeg is distributed in the hope that it will be useful, 00015 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00016 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00017 * Lesser General Public License for more details. 00018 * 00019 * You should have received a copy of the GNU Lesser General Public 00020 * License along with FFmpeg; if not, write to the Free Software 00021 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA 00022 */ 00023 00030 #include <math.h> 00031 #include "libavutil/mathematics.h" 00032 #include "fft.h" 00033 00034 /* sin((M_PI * x / (2*n)) */ 00035 #define SIN(s,n,x) (s->costab[(n) - (x)]) 00036 00037 /* cos((M_PI * x / (2*n)) */ 00038 #define COS(s,n,x) (s->costab[x]) 00039 00040 static void ff_dst_calc_I_c(DCTContext *ctx, FFTSample *data) 00041 { 00042 int n = 1 << ctx->nbits; 00043 int i; 00044 00045 data[0] = 0; 00046 for(i = 1; i < n/2; i++) { 00047 float tmp1 = data[i ]; 00048 float tmp2 = data[n - i]; 00049 float s = SIN(ctx, n, 2*i); 00050 00051 s *= tmp1 + tmp2; 00052 tmp1 = (tmp1 - tmp2) * 0.5f; 00053 data[i ] = s + tmp1; 00054 data[n - i] = s - tmp1; 00055 } 00056 00057 data[n/2] *= 2; 00058 ff_rdft_calc(&ctx->rdft, data); 00059 00060 data[0] *= 0.5f; 00061 00062 for(i = 1; i < n-2; i += 2) { 00063 data[i + 1] += data[i - 1]; 00064 data[i ] = -data[i + 2]; 00065 } 00066 00067 data[n-1] = 0; 00068 } 00069 00070 static void ff_dct_calc_I_c(DCTContext *ctx, FFTSample *data) 00071 { 00072 int n = 1 << ctx->nbits; 00073 int i; 00074 float next = -0.5f * (data[0] - data[n]); 00075 00076 for(i = 0; i < n/2; i++) { 00077 float tmp1 = data[i ]; 00078 float tmp2 = data[n - i]; 00079 float s = SIN(ctx, n, 2*i); 00080 float c = COS(ctx, n, 2*i); 00081 00082 c *= tmp1 - tmp2; 00083 s *= tmp1 - tmp2; 00084 00085 next += c; 00086 00087 tmp1 = (tmp1 + tmp2) * 0.5f; 00088 data[i ] = tmp1 - s; 00089 data[n - i] = tmp1 + s; 00090 } 00091 00092 ff_rdft_calc(&ctx->rdft, data); 00093 data[n] = data[1]; 00094 data[1] = next; 00095 00096 for(i = 3; i <= n; i += 2) 00097 data[i] = data[i - 2] - data[i]; 00098 } 00099 00100 static void ff_dct_calc_III_c(DCTContext *ctx, FFTSample *data) 00101 { 00102 int n = 1 << ctx->nbits; 00103 int i; 00104 00105 float next = data[n - 1]; 00106 float inv_n = 1.0f / n; 00107 00108 for (i = n - 2; i >= 2; i -= 2) { 00109 float val1 = data[i ]; 00110 float val2 = data[i - 1] - data[i + 1]; 00111 float c = COS(ctx, n, i); 00112 float s = SIN(ctx, n, i); 00113 00114 data[i ] = c * val1 + s * val2; 00115 data[i + 1] = s * val1 - c * val2; 00116 } 00117 00118 data[1] = 2 * next; 00119 00120 ff_rdft_calc(&ctx->rdft, data); 00121 00122 for (i = 0; i < n / 2; i++) { 00123 float tmp1 = data[i ] * inv_n; 00124 float tmp2 = data[n - i - 1] * inv_n; 00125 float csc = ctx->csc2[i] * (tmp1 - tmp2); 00126 00127 tmp1 += tmp2; 00128 data[i ] = tmp1 + csc; 00129 data[n - i - 1] = tmp1 - csc; 00130 } 00131 } 00132 00133 static void ff_dct_calc_II_c(DCTContext *ctx, FFTSample *data) 00134 { 00135 int n = 1 << ctx->nbits; 00136 int i; 00137 float next; 00138 00139 for (i=0; i < n/2; i++) { 00140 float tmp1 = data[i ]; 00141 float tmp2 = data[n - i - 1]; 00142 float s = SIN(ctx, n, 2*i + 1); 00143 00144 s *= tmp1 - tmp2; 00145 tmp1 = (tmp1 + tmp2) * 0.5f; 00146 00147 data[i ] = tmp1 + s; 00148 data[n-i-1] = tmp1 - s; 00149 } 00150 00151 ff_rdft_calc(&ctx->rdft, data); 00152 00153 next = data[1] * 0.5; 00154 data[1] *= -1; 00155 00156 for (i = n - 2; i >= 0; i -= 2) { 00157 float inr = data[i ]; 00158 float ini = data[i + 1]; 00159 float c = COS(ctx, n, i); 00160 float s = SIN(ctx, n, i); 00161 00162 data[i ] = c * inr + s * ini; 00163 00164 data[i+1] = next; 00165 00166 next += s * inr - c * ini; 00167 } 00168 } 00169 00170 void ff_dct_calc(DCTContext *s, FFTSample *data) 00171 { 00172 s->dct_calc(s, data); 00173 } 00174 00175 av_cold int ff_dct_init(DCTContext *s, int nbits, enum DCTTransformType inverse) 00176 { 00177 int n = 1 << nbits; 00178 int i; 00179 00180 s->nbits = nbits; 00181 s->inverse = inverse; 00182 00183 ff_init_ff_cos_tabs(nbits+2); 00184 00185 s->costab = ff_cos_tabs[nbits+2]; 00186 00187 s->csc2 = av_malloc(n/2 * sizeof(FFTSample)); 00188 00189 if (ff_rdft_init(&s->rdft, nbits, inverse == DCT_III) < 0) { 00190 av_free(s->csc2); 00191 return -1; 00192 } 00193 00194 for (i = 0; i < n/2; i++) 00195 s->csc2[i] = 0.5 / sin((M_PI / (2*n) * (2*i + 1))); 00196 00197 switch(inverse) { 00198 case DCT_I : s->dct_calc = ff_dct_calc_I_c; break; 00199 case DCT_II : s->dct_calc = ff_dct_calc_II_c ; break; 00200 case DCT_III: s->dct_calc = ff_dct_calc_III_c; break; 00201 case DST_I : s->dct_calc = ff_dst_calc_I_c; break; 00202 } 00203 return 0; 00204 } 00205 00206 av_cold void ff_dct_end(DCTContext *s) 00207 { 00208 ff_rdft_end(&s->rdft); 00209 av_free(s->csc2); 00210 }