1/* 2 * IIR filter 3 * Copyright (c) 2008 Konstantin Shishkov 4 * 5 * This file is part of FFmpeg. 6 * 7 * FFmpeg is free software; you can redistribute it and/or 8 * modify it under the terms of the GNU Lesser General Public 9 * License as published by the Free Software Foundation; either 10 * version 2.1 of the License, or (at your option) any later version. 11 * 12 * FFmpeg is distributed in the hope that it will be useful, 13 * but WITHOUT ANY WARRANTY; without even the implied warranty of 14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 15 * Lesser General Public License for more details. 16 * 17 * You should have received a copy of the GNU Lesser General Public 18 * License along with FFmpeg; if not, write to the Free Software 19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA 20 */ 21 22/** 23 * @file 24 * different IIR filters implementation 25 */ 26 27#include "iirfilter.h" 28#include <math.h> 29 30/** 31 * IIR filter global parameters 32 */ 33typedef struct FFIIRFilterCoeffs{ 34 int order; 35 float gain; 36 int *cx; 37 float *cy; 38}FFIIRFilterCoeffs; 39 40/** 41 * IIR filter state 42 */ 43typedef struct FFIIRFilterState{ 44 float x[1]; 45}FFIIRFilterState; 46 47/// maximum supported filter order 48#define MAXORDER 30 49 50av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, 51 enum IIRFilterMode filt_mode, 52 int order, float cutoff_ratio, 53 float stopband, float ripple) 54{ 55 int i, j; 56 FFIIRFilterCoeffs *c; 57 double wa; 58 double p[MAXORDER + 1][2]; 59 60 if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) 61 return NULL; 62 if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) 63 return NULL; 64 65 c = av_malloc(sizeof(FFIIRFilterCoeffs)); 66 c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); 67 c->cy = av_malloc(sizeof(c->cy[0]) * order); 68 c->order = order; 69 70 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); 71 72 c->cx[0] = 1; 73 for(i = 1; i < (order >> 1) + 1; i++) 74 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; 75 76 p[0][0] = 1.0; 77 p[0][1] = 0.0; 78 for(i = 1; i <= order; i++) 79 p[i][0] = p[i][1] = 0.0; 80 for(i = 0; i < order; i++){ 81 double zp[2]; 82 double th = (i + (order >> 1) + 0.5) * M_PI / order; 83 double a_re, a_im, c_re, c_im; 84 zp[0] = cos(th) * wa; 85 zp[1] = sin(th) * wa; 86 a_re = zp[0] + 2.0; 87 c_re = zp[0] - 2.0; 88 a_im = 89 c_im = zp[1]; 90 zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im); 91 zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im); 92 93 for(j = order; j >= 1; j--) 94 { 95 a_re = p[j][0]; 96 a_im = p[j][1]; 97 p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0]; 98 p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1]; 99 } 100 a_re = p[0][0]*zp[0] - p[0][1]*zp[1]; 101 p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0]; 102 p[0][0] = a_re; 103 } 104 c->gain = p[order][0]; 105 for(i = 0; i < order; i++){ 106 c->gain += p[i][0]; 107 c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) / 108 (p[order][0] * p[order][0] + p[order][1] * p[order][1]); 109 } 110 c->gain /= 1 << order; 111 112 return c; 113} 114 115av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) 116{ 117 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); 118 return s; 119} 120 121#define FILTER(i0, i1, i2, i3) \ 122 in = *src * c->gain \ 123 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ 124 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ 125 res = (s->x[i0] + in )*1 \ 126 + (s->x[i1] + s->x[i3])*4 \ 127 + s->x[i2] *6; \ 128 *dst = av_clip_int16(lrintf(res)); \ 129 s->x[i0] = in; \ 130 src += sstep; \ 131 dst += dstep; \ 132 133void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) 134{ 135 int i; 136 137 if(c->order == 4){ 138 for(i = 0; i < size; i += 4){ 139 float in, res; 140 141 FILTER(0, 1, 2, 3); 142 FILTER(1, 2, 3, 0); 143 FILTER(2, 3, 0, 1); 144 FILTER(3, 0, 1, 2); 145 } 146 }else{ 147 for(i = 0; i < size; i++){ 148 int j; 149 float in, res; 150 in = *src * c->gain; 151 for(j = 0; j < c->order; j++) 152 in += c->cy[j] * s->x[j]; 153 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; 154 for(j = 1; j < c->order >> 1; j++) 155 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; 156 for(j = 0; j < c->order - 1; j++) 157 s->x[j] = s->x[j + 1]; 158 *dst = av_clip_int16(lrintf(res)); 159 s->x[c->order - 1] = in; 160 src += sstep; 161 dst += sstep; 162 } 163 } 164} 165 166av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state) 167{ 168 av_free(state); 169} 170 171av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) 172{ 173 if(coeffs){ 174 av_free(coeffs->cx); 175 av_free(coeffs->cy); 176 } 177 av_free(coeffs); 178} 179 180#ifdef TEST 181#define FILT_ORDER 4 182#define SIZE 1024 183int main(void) 184{ 185 struct FFIIRFilterCoeffs *fcoeffs = NULL; 186 struct FFIIRFilterState *fstate = NULL; 187 float cutoff_coeff = 0.4; 188 int16_t x[SIZE], y[SIZE]; 189 int i; 190 FILE* fd; 191 192 fcoeffs = ff_iir_filter_init_coeffs(FF_FILTER_TYPE_BUTTERWORTH, 193 FF_FILTER_MODE_LOWPASS, FILT_ORDER, 194 cutoff_coeff, 0.0, 0.0); 195 fstate = ff_iir_filter_init_state(FILT_ORDER); 196 197 for (i = 0; i < SIZE; i++) { 198 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); 199 } 200 201 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); 202 203 fd = fopen("in.bin", "w"); 204 fwrite(x, sizeof(x[0]), SIZE, fd); 205 fclose(fd); 206 207 fd = fopen("out.bin", "w"); 208 fwrite(y, sizeof(y[0]), SIZE, fd); 209 fclose(fd); 210 211 ff_iir_filter_free_coeffs(fcoeffs); 212 ff_iir_filter_free_state(fstate); 213 return 0; 214} 215#endif /* TEST */ 216