Libav
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00001 /* 00002 * IIR filter 00003 * Copyright (c) 2008 Konstantin Shishkov 00004 * 00005 * This file is part of FFmpeg. 00006 * 00007 * FFmpeg is free software; you can redistribute it and/or 00008 * modify it under the terms of the GNU Lesser General Public 00009 * License as published by the Free Software Foundation; either 00010 * version 2.1 of the License, or (at your option) any later version. 00011 * 00012 * FFmpeg is distributed in the hope that it will be useful, 00013 * but WITHOUT ANY WARRANTY; without even the implied warranty of 00014 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 00015 * Lesser General Public License for more details. 00016 * 00017 * You should have received a copy of the GNU Lesser General Public 00018 * License along with FFmpeg; if not, write to the Free Software 00019 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 00020 */ 00021 00027 #include "iirfilter.h" 00028 #include <math.h> 00029 00033 typedef struct FFIIRFilterCoeffs{ 00034 int order; 00035 float gain; 00036 int *cx; 00037 float *cy; 00038 }FFIIRFilterCoeffs; 00039 00043 typedef struct FFIIRFilterState{ 00044 float x[1]; 00045 }FFIIRFilterState; 00046 00048 #define MAXORDER 30 00049 00050 av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, 00051 enum IIRFilterMode filt_mode, 00052 int order, float cutoff_ratio, 00053 float stopband, float ripple) 00054 { 00055 int i, j; 00056 FFIIRFilterCoeffs *c; 00057 double wa; 00058 double p[MAXORDER + 1][2]; 00059 00060 if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) 00061 return NULL; 00062 if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) 00063 return NULL; 00064 00065 c = av_malloc(sizeof(FFIIRFilterCoeffs)); 00066 c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); 00067 c->cy = av_malloc(sizeof(c->cy[0]) * order); 00068 c->order = order; 00069 00070 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); 00071 00072 c->cx[0] = 1; 00073 for(i = 1; i < (order >> 1) + 1; i++) 00074 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; 00075 00076 p[0][0] = 1.0; 00077 p[0][1] = 0.0; 00078 for(i = 1; i <= order; i++) 00079 p[i][0] = p[i][1] = 0.0; 00080 for(i = 0; i < order; i++){ 00081 double zp[2]; 00082 double th = (i + (order >> 1) + 0.5) * M_PI / order; 00083 double a_re, a_im, c_re, c_im; 00084 zp[0] = cos(th) * wa; 00085 zp[1] = sin(th) * wa; 00086 a_re = zp[0] + 2.0; 00087 c_re = zp[0] - 2.0; 00088 a_im = 00089 c_im = zp[1]; 00090 zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im); 00091 zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im); 00092 00093 for(j = order; j >= 1; j--) 00094 { 00095 a_re = p[j][0]; 00096 a_im = p[j][1]; 00097 p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0]; 00098 p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1]; 00099 } 00100 a_re = p[0][0]*zp[0] - p[0][1]*zp[1]; 00101 p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0]; 00102 p[0][0] = a_re; 00103 } 00104 c->gain = p[order][0]; 00105 for(i = 0; i < order; i++){ 00106 c->gain += p[i][0]; 00107 c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) / 00108 (p[order][0] * p[order][0] + p[order][1] * p[order][1]); 00109 } 00110 c->gain /= 1 << order; 00111 00112 return c; 00113 } 00114 00115 av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) 00116 { 00117 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); 00118 return s; 00119 } 00120 00121 #define FILTER(i0, i1, i2, i3) \ 00122 in = *src * c->gain \ 00123 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ 00124 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ 00125 res = (s->x[i0] + in )*1 \ 00126 + (s->x[i1] + s->x[i3])*4 \ 00127 + s->x[i2] *6; \ 00128 *dst = av_clip_int16(lrintf(res)); \ 00129 s->x[i0] = in; \ 00130 src += sstep; \ 00131 dst += dstep; \ 00132 00133 void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) 00134 { 00135 int i; 00136 00137 if(c->order == 4){ 00138 for(i = 0; i < size; i += 4){ 00139 float in, res; 00140 00141 FILTER(0, 1, 2, 3); 00142 FILTER(1, 2, 3, 0); 00143 FILTER(2, 3, 0, 1); 00144 FILTER(3, 0, 1, 2); 00145 } 00146 }else{ 00147 for(i = 0; i < size; i++){ 00148 int j; 00149 float in, res; 00150 in = *src * c->gain; 00151 for(j = 0; j < c->order; j++) 00152 in += c->cy[j] * s->x[j]; 00153 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; 00154 for(j = 1; j < c->order >> 1; j++) 00155 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; 00156 for(j = 0; j < c->order - 1; j++) 00157 s->x[j] = s->x[j + 1]; 00158 *dst = av_clip_int16(lrintf(res)); 00159 s->x[c->order - 1] = in; 00160 src += sstep; 00161 dst += sstep; 00162 } 00163 } 00164 } 00165 00166 av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state) 00167 { 00168 av_free(state); 00169 } 00170 00171 av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) 00172 { 00173 if(coeffs){ 00174 av_free(coeffs->cx); 00175 av_free(coeffs->cy); 00176 } 00177 av_free(coeffs); 00178 } 00179 00180 #ifdef TEST 00181 #define FILT_ORDER 4 00182 #define SIZE 1024 00183 int main(void) 00184 { 00185 struct FFIIRFilterCoeffs *fcoeffs = NULL; 00186 struct FFIIRFilterState *fstate = NULL; 00187 float cutoff_coeff = 0.4; 00188 int16_t x[SIZE], y[SIZE]; 00189 int i; 00190 FILE* fd; 00191 00192 fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH, 00193 FF_FILTER_MODE_LOWPASS, FILT_ORDER, 00194 cutoff_coeff, 0.0, 0.0); 00195 fstate = ff_iir_filter_init_state(FILT_ORDER); 00196 00197 for (i = 0; i < SIZE; i++) { 00198 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); 00199 } 00200 00201 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); 00202 00203 fd = fopen("in.bin", "w"); 00204 fwrite(x, sizeof(x[0]), SIZE, fd); 00205 fclose(fd); 00206 00207 fd = fopen("out.bin", "w"); 00208 fwrite(y, sizeof(y[0]), SIZE, fd); 00209 fclose(fd); 00210 00211 ff_iir_filter_free_coeffs(fcoeffs); 00212 ff_iir_filter_free_state(fstate); 00213 return 0; 00214 } 00215 #endif /* TEST */