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00027 #include "iirfilter.h"
00028 #include <complex.h>
00029 #include <math.h>
00030
00034 typedef struct FFIIRFilterCoeffs{
00035 int order;
00036 float gain;
00037 int *cx;
00038 float *cy;
00039 }FFIIRFilterCoeffs;
00040
00044 typedef struct FFIIRFilterState{
00045 float x[1];
00046 }FFIIRFilterState;
00047
00049 #define MAXORDER 30
00050
00051 struct FFIIRFilterCoeffs* ff_iir_filter_init_coeffs(enum IIRFilterType filt_type,
00052 enum IIRFilterMode filt_mode,
00053 int order, float cutoff_ratio,
00054 float stopband, float ripple)
00055 {
00056 int i, j, size;
00057 FFIIRFilterCoeffs *c;
00058 double wa;
00059 complex p[MAXORDER + 1];
00060
00061 if(filt_type != FF_FILTER_TYPE_BUTTERWORTH || filt_mode != FF_FILTER_MODE_LOWPASS)
00062 return NULL;
00063 if(order <= 1 || (order & 1) || order > MAXORDER || cutoff_ratio >= 1.0)
00064 return NULL;
00065
00066 c = av_malloc(sizeof(FFIIRFilterCoeffs));
00067 c->cx = av_malloc(sizeof(c->cx[0]) * ((order >> 1) + 1));
00068 c->cy = av_malloc(sizeof(c->cy[0]) * order);
00069 c->order = order;
00070
00071 wa = 2 * tan(M_PI * 0.5 * cutoff_ratio);
00072
00073 c->cx[0] = 1;
00074 for(i = 1; i < (order >> 1) + 1; i++)
00075 c->cx[i] = c->cx[i - 1] * (order - i + 1LL) / i;
00076
00077 p[0] = 1.0;
00078 for(i = 1; i <= order; i++)
00079 p[i] = 0.0;
00080 for(i = 0; i < order; i++){
00081 complex zp;
00082 double th = (i + (order >> 1) + 0.5) * M_PI / order;
00083 zp = cexp(I*th) * wa;
00084 zp = (zp + 2.0) / (zp - 2.0);
00085
00086 for(j = order; j >= 1; j--)
00087 p[j] = zp*p[j] + p[j - 1];
00088 p[0] *= zp;
00089 }
00090 c->gain = creal(p[order]);
00091 for(i = 0; i < order; i++){
00092 c->gain += creal(p[i]);
00093 c->cy[i] = creal(-p[i] / p[order]);
00094 }
00095 c->gain /= 1 << order;
00096
00097 return c;
00098 }
00099
00100 struct FFIIRFilterState* ff_iir_filter_init_state(int order)
00101 {
00102 FFIIRFilterState* s = av_mallocz(sizeof(FFIIRFilterState) + sizeof(s->x[0]) * (order - 1));
00103 return s;
00104 }
00105
00106 #define FILTER(i0, i1, i2, i3) \
00107 in = *src * c->gain \
00108 + c->cy[0]*s->x[i0] + c->cy[1]*s->x[i1] \
00109 + c->cy[2]*s->x[i2] + c->cy[3]*s->x[i3]; \
00110 res = (s->x[i0] + in )*1 \
00111 + (s->x[i1] + s->x[i3])*4 \
00112 + s->x[i2] *6; \
00113 *dst = av_clip_int16(lrintf(res)); \
00114 s->x[i0] = in; \
00115 src += sstep; \
00116 dst += dstep; \
00117
00118 void ff_iir_filter(const struct FFIIRFilterCoeffs *c, struct FFIIRFilterState *s, int size, const int16_t *src, int sstep, int16_t *dst, int dstep)
00119 {
00120 int i;
00121
00122 if(c->order == 4){
00123 for(i = 0; i < size; i += 4){
00124 float in, res;
00125
00126 FILTER(0, 1, 2, 3);
00127 FILTER(1, 2, 3, 0);
00128 FILTER(2, 3, 0, 1);
00129 FILTER(3, 0, 1, 2);
00130 }
00131 }else{
00132 for(i = 0; i < size; i++){
00133 int j;
00134 float in, res;
00135 in = *src * c->gain;
00136 for(j = 0; j < c->order; j++)
00137 in += c->cy[j] * s->x[j];
00138 res = s->x[0] + in + s->x[c->order >> 1] * c->cx[c->order >> 1];
00139 for(j = 1; j < c->order >> 1; j++)
00140 res += (s->x[j] + s->x[c->order - j]) * c->cx[j];
00141 for(j = 0; j < c->order - 1; j++)
00142 s->x[j] = s->x[j + 1];
00143 *dst = av_clip_int16(lrintf(res));
00144 s->x[c->order - 1] = in;
00145 src += sstep;
00146 dst += sstep;
00147 }
00148 }
00149 }
00150
00151 void ff_iir_filter_free_state(struct FFIIRFilterState *state)
00152 {
00153 av_free(state);
00154 }
00155
00156 void ff_iir_filter_free_coeffs(struct FFIIRFilterCoeffs *coeffs)
00157 {
00158 if(coeffs){
00159 av_free(coeffs->cx);
00160 av_free(coeffs->cy);
00161 }
00162 av_free(coeffs);
00163 }
00164