/* * 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 * different IIR filters implementation */ #include "iirfilter.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 static int butterworth_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c, enum IIRFilterMode filt_mode, int order, float cutoff_ratio, float stopband) { int i, j; double wa; double p[MAXORDER + 1][2]; if (filt_mode != FF_FILTER_MODE_LOWPASS) { av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " "low-pass filter mode\n"); return -1; } if (order & 1) { av_log(avc, AV_LOG_ERROR, "Butterworth filter currently only supports " "even filter orders\n"); return -1; } 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][0] = 1.0; p[0][1] = 0.0; for(i = 1; i <= order; i++) p[i][0] = p[i][1] = 0.0; for(i = 0; i < order; i++){ double zp[2]; double th = (i + (order >> 1) + 0.5) * M_PI / order; double a_re, a_im, c_re, c_im; zp[0] = cos(th) * wa; zp[1] = sin(th) * wa; a_re = zp[0] + 2.0; c_re = zp[0] - 2.0; a_im = c_im = zp[1]; zp[0] = (a_re * c_re + a_im * c_im) / (c_re * c_re + c_im * c_im); zp[1] = (a_im * c_re - a_re * c_im) / (c_re * c_re + c_im * c_im); for(j = order; j >= 1; j--) { a_re = p[j][0]; a_im = p[j][1]; p[j][0] = a_re*zp[0] - a_im*zp[1] + p[j-1][0]; p[j][1] = a_re*zp[1] + a_im*zp[0] + p[j-1][1]; } a_re = p[0][0]*zp[0] - p[0][1]*zp[1]; p[0][1] = p[0][0]*zp[1] + p[0][1]*zp[0]; p[0][0] = a_re; } c->gain = p[order][0]; for(i = 0; i < order; i++){ c->gain += p[i][0]; c->cy[i] = (-p[i][0] * p[order][0] + -p[i][1] * p[order][1]) / (p[order][0] * p[order][0] + p[order][1] * p[order][1]); } c->gain /= 1 << order; return 0; } static int biquad_init_coeffs(void *avc, struct FFIIRFilterCoeffs *c, enum IIRFilterMode filt_mode, int order, float cutoff_ratio, float stopband) { double cos_w0, sin_w0; double a0, x0, x1; if (filt_mode != FF_FILTER_MODE_HIGHPASS && filt_mode != FF_FILTER_MODE_LOWPASS) { av_log(avc, AV_LOG_ERROR, "Biquad filter currently only supports " "high-pass and low-pass filter modes\n"); return -1; } if (order != 2) { av_log(avc, AV_LOG_ERROR, "Biquad filter must have order of 2\n"); return -1; } cos_w0 = cos(M_PI * cutoff_ratio); sin_w0 = sin(M_PI * cutoff_ratio); a0 = 1.0 + (sin_w0 / 2.0); if (filt_mode == FF_FILTER_MODE_HIGHPASS) { c->gain = ((1.0 + cos_w0) / 2.0) / a0; x0 = ((1.0 + cos_w0) / 2.0) / a0; x1 = (-(1.0 + cos_w0)) / a0; } else { // FF_FILTER_MODE_LOWPASS c->gain = ((1.0 - cos_w0) / 2.0) / a0; x0 = ((1.0 - cos_w0) / 2.0) / a0; x1 = (1.0 - cos_w0) / a0; } c->cy[0] = (-1.0 + (sin_w0 / 2.0)) / a0; c->cy[1] = (2.0 * cos_w0) / a0; // divide by gain to make the x coeffs integers. // during filtering, the delay state will include the gain multiplication c->cx[0] = lrintf(x0 / c->gain); c->cx[1] = lrintf(x1 / c->gain); return 0; } av_cold struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(void *avc, enum IIRFilterType filt_type, enum IIRFilterMode filt_mode, int order, float cutoff_ratio, float stopband, float ripple) { FFIIRFilterCoeffs *c; int ret = 0; if (order <= 0 || order > MAXORDER || cutoff_ratio >= 1.0) return NULL; FF_ALLOCZ_OR_GOTO(avc, c, sizeof(FFIIRFilterCoeffs), init_fail); FF_ALLOC_OR_GOTO (avc, c->cx, sizeof(c->cx[0]) * ((order >> 1) + 1), init_fail); FF_ALLOC_OR_GOTO (avc, c->cy, sizeof(c->cy[0]) * order, init_fail); c->order = order; switch (filt_type) { case FF_FILTER_TYPE_BUTTERWORTH: ret = butterworth_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, stopband); break; case FF_FILTER_TYPE_BIQUAD: ret = biquad_init_coeffs(avc, c, filt_mode, order, cutoff_ratio, stopband); break; default: av_log(avc, AV_LOG_ERROR, "filter type is not currently implemented\n"); goto init_fail; } if (!ret) return c; init_fail: ff_iir_filter_free_coeffs(c); return NULL; } av_cold struct FFIIRFilterState* ff_iir_filter_init_state(int order) { FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1)); return s; } #define CONV_S16(dest, source) dest = av_clip_int16(lrintf(source)); #define CONV_FLT(dest, source) dest = source; #define FILTER_BW_O4_1(i0, i1, i2, i3, fmt) \ in = *src0 * 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; \ CONV_##fmt(*dst0, res) \ s->x[i0] = in; \ src0 += sstep; \ dst0 += dstep; #define FILTER_BW_O4(type, fmt) { \ int i; \ const type *src0 = src; \ type *dst0 = dst; \ for (i = 0; i < size; i += 4) { \ float in, res; \ FILTER_BW_O4_1(0, 1, 2, 3, fmt); \ FILTER_BW_O4_1(1, 2, 3, 0, fmt); \ FILTER_BW_O4_1(2, 3, 0, 1, fmt); \ FILTER_BW_O4_1(3, 0, 1, 2, fmt); \ } \ } #define FILTER_DIRECT_FORM_II(type, fmt) { \ int i; \ const type *src0 = src; \ type *dst0 = dst; \ for (i = 0; i < size; i++) { \ int j; \ float in, res; \ in = *src0 * 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]; \ CONV_##fmt(*dst0, res) \ s->x[c->order - 1] = in; \ src0 += sstep; \ dst0 += dstep; \ } \ } #define FILTER_O2(type, fmt) { \ int i; \ const type *src0 = src; \ type *dst0 = dst; \ for (i = 0; i < size; i++) { \ float in = *src0 * c->gain + \ s->x[0] * c->cy[0] + \ s->x[1] * c->cy[1]; \ CONV_##fmt(*dst0, s->x[0] + in + s->x[1] * c->cx[1]) \ s->x[0] = s->x[1]; \ s->x[1] = in; \ src0 += sstep; \ dst0 += 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) { if (c->order == 2) { FILTER_O2(int16_t, S16) } else if (c->order == 4) { FILTER_BW_O4(int16_t, S16) } else { FILTER_DIRECT_FORM_II(int16_t, S16) } } void ff_iir_filter_flt(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const float *src, int sstep, float *dst, int dstep) { if (c->order == 2) { FILTER_O2(float, FLT) } else if (c->order == 4) { FILTER_BW_O4(float, FLT) } else { FILTER_DIRECT_FORM_II(float, FLT) } } av_cold void ff_iir_filter_free_state(struct FFIIRFilterState *state) { av_free(state); } av_cold void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs) { if(coeffs){ av_free(coeffs->cx); av_free(coeffs->cy); } av_free(coeffs); } #ifdef TEST #undef printf #include <stdio.h> #define FILT_ORDER 4 #define SIZE 1024 int main(void) { struct FFIIRFilterCoeffs *fcoeffs = NULL; struct FFIIRFilterState *fstate = NULL; float cutoff_coeff = 0.4; int16_t x[SIZE], y[SIZE]; int i; fcoeffs = ff_iir_filter_init_coeffs(NULL, FF_FILTER_TYPE_BUTTERWORTH, FF_FILTER_MODE_LOWPASS, FILT_ORDER, cutoff_coeff, 0.0, 0.0); fstate = ff_iir_filter_init_state(FILT_ORDER); for (i = 0; i < SIZE; i++) { x[i] = lrint(0.75 * INT16_MAX * sin(0.5*M_PI*i*i/SIZE)); } ff_iir_filter(fcoeffs, fstate, SIZE, x, 1, y, 1); for (i = 0; i < SIZE; i++) printf("%6d %6d\n", x[i], y[i]); ff_iir_filter_free_coeffs(fcoeffs); ff_iir_filter_free_state(fstate); return 0; } #endif /* TEST */