1/* 2 * IIR filter 3 * Copyright (c) 2008 Konstantin Shishkov 4 * 5 * This file is part of Libav. 6 * 7 * Libav 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 * Libav 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 Libav; 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 50static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c, 51 enum IIRFilterMode filt_mode, 52 int order, float cutoff_ratio, 53 float stopband) 54{ 55 int i, j; 56 double wa; 57 double p[MAXORDER + 1][2]; 58 59 if (filt_mode != FF_FILTER_MODE_LOWPASS) { 60 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " 61 "low-pass filter mode\n"); 62 return -1; 63 } 64 if (order & 1) { 65 av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " 66 "even filter orders\n"); 67 return -1; 68 } 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 0; 113} 114 115static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c, 116 enum IIRFilterMode filt_mode, int order, 117 float cutoff_ratio, float stopband) 118{ 119 double cos_w0, sin_w0; 120 double a0, x0, x1; 121 122 if (filt_mode != FF_FILTER_MODE_HIGHPASS && 123 filt_mode != FF_FILTER_MODE_LOWPASS) { 124 av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports " 125 "high-pass and low-pass filter modes\n"); 126 return -1; 127 } 128 if (order != 2) { 129 av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n"); 130 return -1; 131 } 132 133 cos_w0 = cos(M_PI * cutoff_ratio); 134 sin_w0 = sin(M_PI * cutoff_ratio); 135 136 a0 = 1.0 + (sin_w0 / 2.0); 137 138 if (filt_mode == FF_FILTER_MODE_HIGHPASS) { 139 c->gain = ((1.0 + cos_w0) / 2.0) / a0; 140 x0 = ((1.0 + cos_w0) / 2.0) / a0; 141 x1 = (-(1.0 + cos_w0)) / a0; 142 } else { // FF_FILTER_MODE_LOWPASS 143 c->gain = ((1.0 - cos_w0) / 2.0) / a0; 144 x0 = ((1.0 - cos_w0) / 2.0) / a0; 145 x1 = (1.0 - cos_w0) / a0; 146 } 147 c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0; 148 c->cy[1] = (2.0 * cos_w0) / a0; 149 150 // divide by gain to make the x coeffs integers. 151 // during filtering, the delay state will include the gain multiplication 152 c->cx[0] = lrintf(x0 / c->gain); 153 c->cx[1] = lrintf(x1 / c->gain); 154 155 return 0; 156} 157 158av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc, 159 enum IIRFilterType filt_type, 160 enum IIRFilterMode filt_mode, 161 int order, float cutoff_ratio, 162 float stopband, float ripple) 163{ 164 FFIIRFilterCoeffs *c; 165 int ret = 0; 166 167 if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0) 168 return NULL; 169 170 FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs), 171 init_fail); 172 FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1), 173 init_fail); 174 FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order, 175 init_fail); 176 c->order = order; 177 178 switch (filt_type) { 179 case FF_FILTER_TYPE_BUTTERWORTH: 180 ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, 181 stopband); 182 break; 183 case FF_FILTER_TYPE_BIQUAD: 184 ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, 185 stopband); 186 break; 187 default: 188 av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n"); 189 goto init_fail; 190 } 191 192 if (!ret) 193 return c; 194 195init_fail: 196 ff_iir_filter_free_coeffs(c); 197 return NULL; 198} 199 200av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) 201{ 202 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); 203 return s; 204} 205 206#define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source)); 207 208#define CONV_FLT(dest, source) dest = source; 209 210#define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \ 211 in = *src0 * c->gain \ 212 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ 213 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ 214 res = (s->x[i0] + in )*1 \ 215 + (s->x[i1] + s->x[i3])*4 \ 216 + s->x[i2] *6; \ 217 CONV_##fmt(*dst0, res) \ 218 s->x[i0] = in; \ 219 src0 += sstep; \ 220 dst0 += dstep; 221 222#define FILTER_BW_O4(type, fmt) { \ 223 int i; \ 224 const type *src0 = src; \ 225 type *dst0 = dst; \ 226 for (i = 0; i < size; i += 4) { \ 227 float in, res; \ 228 FILTER_BW_O4_1(0, 1, 2, 3, fmt); \ 229 FILTER_BW_O4_1(1, 2, 3, 0, fmt); \ 230 FILTER_BW_O4_1(2, 3, 0, 1, fmt); \ 231 FILTER_BW_O4_1(3, 0, 1, 2, fmt); \ 232 } \ 233} 234 235#define FILTER_DIRECT_FORM_II(type, fmt) { \ 236 int i; \ 237 const type *src0 = src; \ 238 type *dst0 = dst; \ 239 for (i = 0; i < size; i++) { \ 240 int j; \ 241 float in, res; \ 242 in = *src0 * c->gain; \ 243 for(j = 0; j < c->order; j++) \ 244 in += c->cy[j] * s->x[j]; \ 245 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \ 246 for(j = 1; j < c->order >> 1; j++) \ 247 res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \ 248 for(j = 0; j < c->order - 1; j++) \ 249 s->x[j] = s->x[j + 1]; \ 250 CONV_##fmt(*dst0, res) \ 251 s->x[c->order - 1] = in; \ 252 src0 += sstep; \ 253 dst0 += dstep; \ 254 } \ 255} 256 257#define FILTER_O2(type, fmt) { \ 258 int i; \ 259 const type *src0 = src; \ 260 type *dst0 = dst; \ 261 for (i = 0; i < size; i++) { \ 262 float in = *src0 * c->gain + \ 263 s->x[0] * c->cy[0] + \ 264 s->x[1] * c->cy[1]; \ 265 CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \ 266 s->x[0] = s->x[1]; \ 267 s->x[1] = in; \ 268 src0 += sstep; \ 269 dst0 += dstep; \ 270 } \ 271} 272 273void ff_iir_filter(const struct FFIIRFilterCoeffs *c, 274 struct FFIIRFilterState *s, int size, 275 const int16_t *src, int sstep, int16_t *dst, int dstep) 276{ 277 if (c->order == 2) { 278 FILTER_O2(int16_t, S16) 279 } else if (c->order == 4) { 280 FILTER_BW_O4(int16_t, S16) 281 } else { 282 FILTER_DIRECT_FORM_II(int16_t, S16) 283 } 284} 285 286void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c, 287 struct FFIIRFilterState *s, int size, 288 const float *src, int sstep, float *dst, int dstep) 289{ 290 if (c->order == 2) { 291 FILTER_O2(float, FLT) 292 } else if (c->order == 4) { 293 FILTER_BW_O4(float, FLT) 294 } else { 295 FILTER_DIRECT_FORM_II(float, FLT) 296 } 297} 298 299av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state) 300{ 301 av_free(state); 302} 303 304av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) 305{ 306 if(coeffs){ 307 av_free(coeffs->cx); 308 av_free(coeffs->cy); 309 } 310 av_free(coeffs); 311} 312 313#ifdef TEST 314#undef printf 315#include <stdio.h> 316 317#define FILT_ORDER 4 318#define SIZE 1024 319int main(void) 320{ 321 struct FFIIRFilterCoeffs *fcoeffs = NULL; 322 struct FFIIRFilterState *fstate = NULL; 323 float cutoff_coeff = 0.4; 324 int16_t x[SIZE], y[SIZE]; 325 int i; 326 327 fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH, 328 FF_FILTER_MODE_LOWPASS, FILT_ORDER, 329 cutoff_coeff, 0.0, 0.0); 330 fstate = ff_iir_filter_init_state(FILT_ORDER); 331 332 for (i = 0; i < SIZE; i++) { 333 x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); 334 } 335 336 ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); 337 338 for (i = 0; i < SIZE; i++) 339 printf("%6d %6d\n", x[i], y[i]); 340 341 ff_iir_filter_free_coeffs(fcoeffs); 342 ff_iir_filter_free_state(fstate); 343 return 0; 344} 345#endif /* TEST */ 346