/* * IIR filter * Copyright (c) 2008 Konstantin Shishkov * * This file is part of FFmpeg. * * FFmpeg is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * FFmpeg is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with FFmpeg; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file iirfilter.c * different IIR filters implementation */ #include "iirfilter.h" #include <complex.h> #include <math.h> /** * IIR filter global parameters */ typedef struct FFIIRFilterCoeffs{ int order; float gain; int *cx; float *cy; }FFIIRFilterCoeffs; /** * IIR filter state */ typedef struct FFIIRFilterState{ float x[1]; }FFIIRFilterState; /// maximum supported filter order #define MAXORDER 30 struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type, enum IIRFilterMode filt_mode, int order, float cutoff_ratio, float stopband, float ripple) { int i, j, size; FFIIRFilterCoeffs *c; double wa; complex p[MAXORDER + 1]; if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS) return NULL; if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0) return NULL; c = av_malloc(sizeof(FFIIRFilterCoeffs)); c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1)); c->cy = av_malloc(sizeof(c->cy[0]) * order); c->order = order; wa = 2 * tan(M_PI * 0.5 * cutoff_ratio); c->cx[0] = 1; for(i = 1; i < (order >> 1) + 1; i++) c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i; p[0] = 1.0; for(i = 1; i <= order; i++) p[i] = 0.0; for(i = 0; i < order; i++){ complex zp; double th = (i + (order >> 1) + 0.5) * M_PI / order; zp = cexp(I*th) * wa; zp = (zp + 2.0) / (zp - 2.0); for(j = order; j >= 1; j--) p[j] = zp*p[j] + p[j - 1]; p[0] *= zp; } c->gain = creal(p[order]); for(i = 0; i < order; i++){ c->gain += creal(p[i]); c->cy[i] = creal(-p[i] / p[order]); } c->gain /= 1 << order; return c; } struct FFIIRFilterState* ff_iir_filter_init_state(int order) { FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); return s; } #define FILTER(i0, i1, i2, i3) \ in = *src * c->gain \ + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \ + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \ res = (s->x[i0] + in )*1 \ + (s->x[i1] + s->x[i3])*4 \ + s->x[i2] *6; \ *dst = av_clip_int16(lrintf(res)); \ s->x[i0] = in; \ src += sstep; \ dst += dstep; \ void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep) { int i; if(c->order == 4){ for(i = 0; i < size; i += 4){ float in, res; FILTER(0, 1, 2, 3); FILTER(1, 2, 3, 0); FILTER(2, 3, 0, 1); FILTER(3, 0, 1, 2); } }else{ for(i = 0; i < size; i++){ int j; float in, res; in = *src * c->gain; for(j = 0; j < c->order; j++) in += c->cy[j] * s->x[j]; res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1]; for(j = 1; j < c->order >> 1; j++) res += (s->x[j] + s->x[c->order - j]) * c->cx[j]; for(j = 0; j < c->order - 1; j++) s->x[j] = s->x[j + 1]; *dst = av_clip_int16(lrintf(res)); s->x[c->order - 1] = in; src += sstep; dst += sstep; } } } void ff_iir_filter_free_state(struct FFIIRFilterState *state) { av_free(state); } void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) { if(coeffs){ av_free(coeffs->cx); av_free(coeffs->cy); } av_free(coeffs); }