Add generic IIR filter interface with Butterworth lowpass filter implementation

and remove obsoleted old lowpass filter.

Originally committed as revision 15005 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/iirfilter.c

@@ -0,0 +1,164 @@
+/*
+ * 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);
+}
+