| 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 | #include "libavutil/attributes.h" |
| 30 | #include "libavutil/common.h" |
| 31 | |
| 32 | /** |
| 33 | * IIR filter global parameters |
| 34 | */ |
| 35 | typedef struct FFIIRFilterCoeffs{ |
| 36 | int order; |
| 37 | float gain; |
| 38 | int *cx; |
| 39 | float *cy; |
| 40 | }FFIIRFilterCoeffs; |
| 41 | |
| 42 | /** |
| 43 | * IIR filter state |
| 44 | */ |
| 45 | typedef struct FFIIRFilterState{ |
| 46 | float x[1]; |
| 47 | }FFIIRFilterState; |
| 48 | |
| 49 | /// maximum supported filter order |
| 50 | #define MAXORDER 30 |
| 51 | |
| 52 | static av_cold int butterworth_init_coeffs(void *avc, |
| 53 | struct FFIIRFilterCoeffs *c, |
| 54 | enum IIRFilterMode filt_mode, |
| 55 | int order, float cutoff_ratio, |
| 56 | float stopband) |
| 57 | { |
| 58 | int i, j; |
| 59 | double wa; |
| 60 | double p[MAXORDER + 1][2]; |
| 61 | |
| 62 | if (filt_mode != FF_FILTER_MODE_LOWPASS) { |
| 63 | av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " |
| 64 | "low-pass filter mode\n"); |
| 65 | return -1; |
| 66 | } |
| 67 | if (order & 1) { |
| 68 | av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " |
| 69 | "even filter orders\n"); |
| 70 | return -1; |
| 71 | } |
| 72 | |
| 73 | wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); |
| 74 | |
| 75 | c->cx[0] = 1; |
| 76 | for(i = 1; i < (order >> 1) + 1; i++) |
| 77 | c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; |
| 78 | |
| 79 | p[0][0] = 1.0; |
| 80 | p[0][1] = 0.0; |
| 81 | for(i = 1; i <= order; i++) |
| 82 | p[i][0] = p[i][1] = 0.0; |
| 83 | for(i = 0; i < order; i++){ |
| 84 | double zp[2]; |
| 85 | double th = (i + (order >> 1) + 0.5) * M_PI / order; |
| 86 | double a_re, a_im, c_re, c_im; |
| 87 | zp[0] = cos(th) * wa; |
| 88 | zp[1] = sin(th) * wa; |
| 89 | a_re = zp[0] + 2.0; |
| 90 | c_re = zp[0] - 2.0; |
| 91 | a_im = |
| 92 | c_im = zp[1]; |
| 93 | zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im); |
| 94 | zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im); |
| 95 | |
| 96 | for(j = order; j >= 1; j--) |
| 97 | { |
| 98 | a_re = p[j][0]; |
| 99 | a_im = p[j][1]; |
| 100 | p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0]; |
| 101 | p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1]; |
| 102 | } |
| 103 | a_re = p[0][0]*zp[0] - p[0][1]*zp[1]; |
| 104 | p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0]; |
| 105 | p[0][0] = a_re; |
| 106 | } |
| 107 | c->gain = p[order][0]; |
| 108 | for(i = 0; i < order; i++){ |
| 109 | c->gain += p[i][0]; |
| 110 | c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) / |
| 111 | (p[order][0] * p[order][0] + p[order][1] * p[order][1]); |
| 112 | } |
| 113 | c->gain /= 1 << order; |
| 114 | |
| 115 | return 0; |
| 116 | } |
| 117 | |
| 118 | static av_cold int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c, |
| 119 | enum IIRFilterMode filt_mode, int order, |
| 120 | float cutoff_ratio, float stopband) |
| 121 | { |
| 122 | double cos_w0, sin_w0; |
| 123 | double a0, x0, x1; |
| 124 | |
| 125 | if (filt_mode != FF_FILTER_MODE_HIGHPASS && |
| 126 | filt_mode != FF_FILTER_MODE_LOWPASS) { |
| 127 | av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports " |
| 128 | "high-pass and low-pass filter modes\n"); |
| 129 | return -1; |
| 130 | } |
| 131 | if (order != 2) { |
| 132 | av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n"); |
| 133 | return -1; |
| 134 | } |
| 135 | |
| 136 | cos_w0 = cos(M_PI * cutoff_ratio); |
| 137 | sin_w0 = sin(M_PI * cutoff_ratio); |
| 138 | |
| 139 | a0 = 1.0 + (sin_w0 / 2.0); |
| 140 | |
| 141 | if (filt_mode == FF_FILTER_MODE_HIGHPASS) { |
| 142 | c->gain = ((1.0 + cos_w0) / 2.0) / a0; |
| 143 | x0 = ((1.0 + cos_w0) / 2.0) / a0; |
| 144 | x1 = (-(1.0 + cos_w0)) / a0; |
| 145 | } else { // FF_FILTER_MODE_LOWPASS |
| 146 | c->gain = ((1.0 - cos_w0) / 2.0) / a0; |
| 147 | x0 = ((1.0 - cos_w0) / 2.0) / a0; |
| 148 | x1 = (1.0 - cos_w0) / a0; |
| 149 | } |
| 150 | c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0; |
| 151 | c->cy[1] = (2.0 * cos_w0) / a0; |
| 152 | |
| 153 | // divide by gain to make the x coeffs integers. |
| 154 | // during filtering, the delay state will include the gain multiplication |
| 155 | c->cx[0] = lrintf(x0 / c->gain); |
| 156 | c->cx[1] = lrintf(x1 / c->gain); |
| 157 | |
| 158 | return 0; |
| 159 | } |
| 160 | |
| 161 | av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc, |
| 162 | enum IIRFilterType filt_type, |
| 163 | enum IIRFilterMode filt_mode, |
| 164 | int order, float cutoff_ratio, |
| 165 | float stopband, float ripple) |
| 166 | { |
| 167 | FFIIRFilterCoeffs *c; |
| 168 | int ret = 0; |
| 169 | |
| 170 | if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0) |
| 171 | return NULL; |
| 172 | |
| 173 | FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs), |
| 174 | init_fail); |
| 175 | FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1), |
| 176 | init_fail); |
| 177 | FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order, |
| 178 | init_fail); |
| 179 | c->order = order; |
| 180 | |
| 181 | switch (filt_type) { |
| 182 | case FF_FILTER_TYPE_BUTTERWORTH: |
| 183 | ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, |
| 184 | stopband); |
| 185 | break; |
| 186 | case FF_FILTER_TYPE_BIQUAD: |
| 187 | ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, |
| 188 | stopband); |
| 189 | break; |
| 190 | default: |
| 191 | av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n"); |
| 192 | goto init_fail; |
| 193 | } |
| 194 | |
| 195 | if (!ret) |
| 196 | return c; |
| 197 | |
| 198 | init_fail: |
| 199 | ff_iir_filter_free_coeffsp(&c); |
| 200 | return NULL; |
| 201 | } |
| 202 | |
| 203 | av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) |
| 204 | { |
| 205 | FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); |
| 206 | return s; |
| 207 | } |
| 208 | |
| 209 | #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source)); |
| 210 | |
| 211 | #define CONV_FLT(dest, source) dest = source; |
| 212 | |
| 213 | #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \ |
| 214 | in = *src0 * c->gain \ |
| 215 | + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ |
| 216 | + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ |
| 217 | res = (s->x[i0] + in )*1 \ |
| 218 | + (s->x[i1] + s->x[i3])*4 \ |
| 219 | + s->x[i2] *6; \ |
| 220 | CONV_##fmt(*dst0, res) \ |
| 221 | s->x[i0] = in; \ |
| 222 | src0 += sstep; \ |
| 223 | dst0 += dstep; |
| 224 | |
| 225 | #define FILTER_BW_O4(type, fmt) { \ |
| 226 | int i; \ |
| 227 | const type *src0 = src; \ |
| 228 | type *dst0 = dst; \ |
| 229 | for (i = 0; i < size; i += 4) { \ |
| 230 | float in, res; \ |
| 231 | FILTER_BW_O4_1(0, 1, 2, 3, fmt); \ |
| 232 | FILTER_BW_O4_1(1, 2, 3, 0, fmt); \ |
| 233 | FILTER_BW_O4_1(2, 3, 0, 1, fmt); \ |
| 234 | FILTER_BW_O4_1(3, 0, 1, 2, fmt); \ |
| 235 | } \ |
| 236 | } |
| 237 | |
| 238 | #define FILTER_DIRECT_FORM_II(type, fmt) { \ |
| 239 | int i; \ |
| 240 | const type *src0 = src; \ |
| 241 | type *dst0 = dst; \ |
| 242 | for (i = 0; i < size; i++) { \ |
| 243 | int j; \ |
| 244 | float in, res; \ |
| 245 | in = *src0 * c->gain; \ |
| 246 | for(j = 0; j < c->order; j++) \ |
| 247 | in += c->cy[j] * s->x[j]; \ |
| 248 | res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; \ |
| 249 | for(j = 1; j < c->order >> 1; j++) \ |
| 250 | res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; \ |
| 251 | for(j = 0; j < c->order - 1; j++) \ |
| 252 | s->x[j] = s->x[j + 1]; \ |
| 253 | CONV_##fmt(*dst0, res) \ |
| 254 | s->x[c->order - 1] = in; \ |
| 255 | src0 += sstep; \ |
| 256 | dst0 += dstep; \ |
| 257 | } \ |
| 258 | } |
| 259 | |
| 260 | #define FILTER_O2(type, fmt) { \ |
| 261 | int i; \ |
| 262 | const type *src0 = src; \ |
| 263 | type *dst0 = dst; \ |
| 264 | for (i = 0; i < size; i++) { \ |
| 265 | float in = *src0 * c->gain + \ |
| 266 | s->x[0] * c->cy[0] + \ |
| 267 | s->x[1] * c->cy[1]; \ |
| 268 | CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \ |
| 269 | s->x[0] = s->x[1]; \ |
| 270 | s->x[1] = in; \ |
| 271 | src0 += sstep; \ |
| 272 | dst0 += dstep; \ |
| 273 | } \ |
| 274 | } |
| 275 | |
| 276 | void ff_iir_filter(const struct FFIIRFilterCoeffs *c, |
| 277 | struct FFIIRFilterState *s, int size, |
| 278 | const int16_t *src, int sstep, int16_t *dst, int dstep) |
| 279 | { |
| 280 | if (c->order == 2) { |
| 281 | FILTER_O2(int16_t, S16) |
| 282 | } else if (c->order == 4) { |
| 283 | FILTER_BW_O4(int16_t, S16) |
| 284 | } else { |
| 285 | FILTER_DIRECT_FORM_II(int16_t, S16) |
| 286 | } |
| 287 | } |
| 288 | |
| 289 | void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c, |
| 290 | struct FFIIRFilterState *s, int size, |
| 291 | const float *src, int sstep, float *dst, int dstep) |
| 292 | { |
| 293 | if (c->order == 2) { |
| 294 | FILTER_O2(float, FLT) |
| 295 | } else if (c->order == 4) { |
| 296 | FILTER_BW_O4(float, FLT) |
| 297 | } else { |
| 298 | FILTER_DIRECT_FORM_II(float, FLT) |
| 299 | } |
| 300 | } |
| 301 | |
| 302 | av_cold void ff_iir_filter_free_statep(struct FFIIRFilterState **state) |
| 303 | { |
| 304 | av_freep(state); |
| 305 | } |
| 306 | |
| 307 | av_cold void ff_iir_filter_free_coeffsp(struct FFIIRFilterCoeffs **coeffsp) |
| 308 | { |
| 309 | struct FFIIRFilterCoeffs *coeffs = *coeffsp; |
| 310 | if(coeffs){ |
| 311 | av_freep(&coeffs->cx); |
| 312 | av_freep(&coeffs->cy); |
| 313 | } |
| 314 | av_freep(coeffsp); |
| 315 | } |
| 316 | |
| 317 | void ff_iir_filter_init(FFIIRFilterContext *f) { |
| 318 | f->filter_flt = ff_iir_filter_flt; |
| 319 | |
| 320 | if (HAVE_MIPSFPU) |
| 321 | ff_iir_filter_init_mips(f); |
| 322 | } |
| 323 | |
| 324 | #ifdef TEST |
| 325 | #include <stdio.h> |
| 326 | |
| 327 | #define FILT_ORDER 4 |
| 328 | #define SIZE 1024 |
| 329 | int main(void) |
| 330 | { |
| 331 | struct FFIIRFilterCoeffs *fcoeffs = NULL; |
| 332 | struct FFIIRFilterState *fstate = NULL; |
| 333 | float cutoff_coeff = 0.4; |
| 334 | int16_t x[SIZE], y[SIZE]; |
| 335 | int i; |
| 336 | |
| 337 | fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH, |
| 338 | FF_FILTER_MODE_LOWPASS, FILT_ORDER, |
| 339 | cutoff_coeff, 0.0, 0.0); |
| 340 | fstate = ff_iir_filter_init_state(FILT_ORDER); |
| 341 | |
| 342 | for (i = 0; i < SIZE; i++) { |
| 343 | x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); |
| 344 | } |
| 345 | |
| 346 | ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); |
| 347 | |
| 348 | for (i = 0; i < SIZE; i++) |
| 349 | printf("%6d %6d\n", x[i], y[i]); |
| 350 | |
| 351 | ff_iir_filter_free_coeffsp(&fcoeffs); |
| 352 | ff_iir_filter_free_statep(&fstate); |
| 353 | return 0; |
| 354 | } |
| 355 | #endif /* TEST */ |