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diff --git a/flow/gsl/gslfilter.h b/flow/gsl/gslfilter.h
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+/* GSL - Generic Sound Layer
+ * Copyright (C) 2001 Stefan Westerfeld and Tim Janik
+ *
+ * This library 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 of the License, or (at your option) any later version.
+ *
+ * This library 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 this library; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place, Suite 330,
+ * Boston, MA 02111-1307, USA.
+ */
+#ifndef __GSL_FILTER_H__
+#define __GSL_FILTER_H__
+
+#include <gsl/gslmath.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+
+/* --- transformations --- */
+static inline GslComplex gsl_trans_s2z (GslComplex s);
+static inline double gsl_trans_freq2s (double w);
+static inline double gsl_trans_zepsilon2ss (double epsilon);
+
+
+/* --- filter roots and poles --- */
+void gsl_filter_butter_rp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ GslComplex *roots, /* [0..iorder-1] */
+ GslComplex *poles);
+void gsl_filter_tscheb1_rp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ GslComplex *roots, /* [0..iorder-1] */
+ GslComplex *poles);
+void gsl_filter_tscheb2_rp (unsigned int iorder,
+ double c_freq, /* 0..pi */
+ double steepness,
+ double epsilon,
+ GslComplex *roots, /* [0..iorder-1] */
+ GslComplex *poles);
+
+
+/* --- tschebyscheff type II steepness --- */
+double gsl_filter_tscheb2_steepness_db (unsigned int iorder,
+ double c_freq,
+ double epsilon,
+ double stopband_db);
+double gsl_filter_tscheb2_steepness (unsigned int iorder,
+ double c_freq,
+ double epsilon,
+ double residue);
+
+
+/* --- lowpass filters --- */
+void gsl_filter_butter_lp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb1_lp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb2_lp (unsigned int iorder,
+ double c_freq, /* 0..pi */
+ double steepness,
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+
+
+/* --- highpass filters --- */
+void gsl_filter_butter_hp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb1_hp (unsigned int iorder,
+ double freq, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb2_hp (unsigned int iorder,
+ double c_freq, /* 0..pi */
+ double steepness,
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+
+
+/* --- bandpass filters --- */
+void gsl_filter_butter_bp (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb1_bp (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb2_bp (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double steepness,
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+
+
+/* --- bandstop filters --- */
+void gsl_filter_butter_bs (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb1_bs (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+void gsl_filter_tscheb2_bs (unsigned int iorder,
+ double freq1, /* 0..pi */
+ double freq2, /* 0..pi */
+ double steepness,
+ double epsilon,
+ double *a, /* [0..iorder] */
+ double *b);
+
+
+/* --- FIR Filters --- */
+void gsl_filter_fir_approx (unsigned int iorder,
+ double *a, /* [0..iorder] */
+ unsigned int n_points,
+ const double *freq,
+ const double *value);
+
+
+/* --- IIR Filter Evaluation --- */
+typedef struct {
+ guint order;
+ gdouble *a; /* [0..order] */
+ gdouble *b; /* [0..order] */
+ gdouble *w; /* [0..2*order] */
+} GslIIRFilter;
+void gsl_iir_filter_setup (GslIIRFilter *f,
+ guint order,
+ const gdouble *a,
+ const gdouble *b,
+ gdouble *buffer); /* 4*(order+1) */
+void gsl_iir_filter_change (GslIIRFilter *f,
+ guint order,
+ const gdouble *a,
+ const gdouble *b,
+ gdouble *buffer); /* 4*(order+1) */
+void gsl_iir_filter_eval (GslIIRFilter *f,
+ guint n_values,
+ const gfloat *x,
+ gfloat *y);
+
+
+/* --- Biquad Filters --- */
+typedef enum /*< skip >*/
+{
+ GSL_BIQUAD_NORMALIZE_PASSBAND,
+ GSL_BIQUAD_NORMALIZE_RESONANCE_GAIN,
+ GSL_BIQUAD_NORMALIZE_PEAK_GAIN
+} GslBiquadNormalize;
+
+typedef enum /*< skip >*/
+{
+ GSL_BIQUAD_RESONANT_LOWPASS = 1,
+ GSL_BIQUAD_RESONANT_HIGHPASS,
+ GSL_BIQUAD_LOWSHELVE,
+ GSL_BIQUAD_HIGHSHELVE,
+ GSL_BIQUAD_PEAK
+} GslBiquadType;
+
+typedef struct {
+ GslBiquadType type;
+ GslBiquadNormalize normalize; /* high/low pass */
+ gfloat f_fn;
+ gfloat gain;
+ gfloat quality; /* peak/notch */
+ guint dirty : 1; /* post filter_config() changes? */
+ guint approx_values : 1; /* biquad_config_approx_*() called? */
+ /*< private >*/
+ gdouble k, v;
+} GslBiquadConfig;
+
+typedef struct {
+ gdouble xc0, xc1, xc2;
+ gdouble yc1, yc2; /* yc0==1 */
+ gdouble xd1, xd2, yd1, yd2; /* history */
+} GslBiquadFilter;
+
+void gsl_biquad_config_init (GslBiquadConfig *c,
+ GslBiquadType type,
+ GslBiquadNormalize normalize);
+void gsl_biquad_config_setup (GslBiquadConfig *c,
+ gfloat f_fn,
+ gfloat gain,
+ gfloat quality);
+void gsl_biquad_config_approx_freq (GslBiquadConfig *c,
+ gfloat f_fn);
+void gsl_biquad_config_approx_gain (GslBiquadConfig *c,
+ gfloat gain);
+void gsl_biquad_filter_config (GslBiquadFilter *f,
+ GslBiquadConfig *c,
+ gboolean reset_state);
+void gsl_biquad_filter_eval (GslBiquadFilter *f,
+ guint n_values,
+ const gfloat *x,
+ gfloat *y);
+
+
+/* --- filter scanning -- */
+gdouble gsl_filter_sine_scan (guint order,
+ const gdouble *a,
+ const gdouble *b,
+ gdouble freq,
+ guint n_values);
+
+
+/* --- implementations --- */
+static inline GslComplex
+gsl_trans_s2z (GslComplex s)
+{
+ /* 1 + (Td/2) * s
+ * z = ----------------
+ * 1 - (Td/2) * s
+ */
+ GslComplex one = { 1, 0 };
+ return gsl_complex_div (gsl_complex_add (one, s), gsl_complex_sub (one, s));
+ /* return gsl_complex_div (gsl_complex_sub (s, one), gsl_complex_add (s, one)); */
+}
+static inline double
+gsl_trans_freq2s (double w)
+{
+ return tan (w / 2.);
+}
+static inline double
+gsl_trans_zepsilon2ss (double zepsilon)
+{
+ double e2 = (1.0 - zepsilon) * (1.0 - zepsilon);
+ /* 1___ _________________
+ * | \ | 1.0
+ * |-----\<---- 1 - zepsilon zepsilon = \ | ----------------
+ * |_______\________________ \| 1 + sepsilon^2
+ */
+ return sqrt ((1.0 - e2) / e2);
+}
+static inline double
+gsl_trans_freq2z (double w)
+{
+ return atan (w) * 2.;
+}
+
+
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* __GSL_FILTER_H__ */ /* vim:set ts=8 sw=2 sts=2: */
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