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 libavcodec/iirfilter.c 24 * different IIR filters implementation 25 */ 26 27#include "iirfilter.h" 28#include <complex.h> 29#include <math.h> 30 31/** 32 * IIR filter global parameters 33 */ 34typedef struct FFIIRFilterCoeffs{ 35 int order; 36 float gain; 37 int *cx; 38 float *cy; 39}FFIIRFilterCoeffs; 40 41/** 42 * IIR filter state 43 */ 44typedef struct FFIIRFilterState{ 45 float x[1]; 46}FFIIRFilterState; 47 48/// maximum supported filter order 49#define MAXORDER 30 50 51struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, 52 enum IIRFilterMode filt_mode, 53 int order, float cutoff_ratio, 54 float stopband, float ripple) 55{ 56 int i, j, size; 57 FFIIRFilterCoeffs *c; 58 double wa; 59 complex p[MAXORDER + 1]; 60 61 if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) 62 return NULL; 63 if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) 64 return NULL; 65 66 c = av_malloc(sizeof(FFIIRFilterCoeffs)); 67 c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); 68 c->cy = av_malloc(sizeof(c->cy[0]) * order); 69 c->order = order; 70 71 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); 72 73 c->cx[0] = 1; 74 for(i = 1; i < (order >> 1) + 1; i++) 75 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; 76 77 p[0] = 1.0; 78 for(i = 1; i <= order; i++) 79 p[i] = 0.0; 80 for(i = 0; i < order; i++){ 81 complex zp; 82 double th = (i + (order >> 1) + 0.5) * M_PI / order; 83 zp = cexp(I*th) * wa; 84 zp = (zp + 2.0) / (zp - 2.0); 85 86 for(j = order; j >= 1; j--) 87 p[j] = zp*p[j] + p[j - 1]; 88 p[0] *= zp; 89 } 90 c->gain = creal(p[order]); 91 for(i = 0; i < order; i++){ 92 c->gain += creal(p[i]); 93 c->cy[i] = creal(-p[i] / p[order]); 94 } 95 c->gain /= 1 << order; 96 97 return c; 98} 99 100struct FFIIRFilterState* ff_iir_filter_init_state(int order) 101{ 102 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); 103 return s; 104} 105 106#define FILTER(i0, i1, i2, i3) \ 107 in = *src * c->gain \ 108 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ 109 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ 110 res = (s->x[i0] + in )*1 \ 111 + (s->x[i1] + s->x[i3])*4 \ 112 + s->x[i2] *6; \ 113 *dst = av_clip_int16(lrintf(res)); \ 114 s->x[i0] = in; \ 115 src += sstep; \ 116 dst += dstep; \ 117 118void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) 119{ 120 int i; 121 122 if(c->order == 4){ 123 for(i = 0; i < size; i += 4){ 124 float in, res; 125 126 FILTER(0, 1, 2, 3); 127 FILTER(1, 2, 3, 0); 128 FILTER(2, 3, 0, 1); 129 FILTER(3, 0, 1, 2); 130 } 131 }else{ 132 for(i = 0; i < size; i++){ 133 int j; 134 float in, res; 135 in = *src * c->gain; 136 for(j = 0; j < c->order; j++) 137 in += c->cy[j] * s->x[j]; 138 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; 139 for(j = 1; j < c->order >> 1; j++) 140 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; 141 for(j = 0; j < c->order - 1; j++) 142 s->x[j] = s->x[j + 1]; 143 *dst = av_clip_int16(lrintf(res)); 144 s->x[c->order - 1] = in; 145 src += sstep; 146 dst += sstep; 147 } 148 } 149} 150 151void ff_iir_filter_free_state(struct FFIIRFilterState *state) 152{ 153 av_free(state); 154} 155 156void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) 157{ 158 if(coeffs){ 159 av_free(coeffs->cx); 160 av_free(coeffs->cy); 161 } 162 av_free(coeffs); 163} 164 165