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+/* GSL - Generic Sound Layer
+ * Copyright (C) 2001 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_FFT_H__
+#define __GSL_FFT_H__
+
+#include <gsl/gsldefs.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+
+/**
+ * gsl_power2_fftac
+ * @n_values:      Number of complex values
+ * @ri_values_in:  Complex sample values [0..n_values*2-1]
+ * @ri_values_out: Complex frequency values [0..n_values*2-1]
+ * This function performs a decimation in time fourier transformation
+ * in forward direction, where the input values are equidistant sampled
+ * data, and the output values contain the frequency proportions of the
+ * input.
+ * The input and output arrays are complex values with real and imaginery
+ * portions interleaved, adressable in the range [0..2*n_values-1], where
+ * n_values must be a power of two.
+ * Frequencies are stored in-order, the K-th output corresponds to the
+ * frequency K/n_values. (If you want to interpret negative frequencies,
+ * note that the frequencies -K/n_values and (n_values-K)/n_values are
+ * equivalent).
+ * Note that the transformation is performed out of place, the input
+ * array is not modified, and may not overlap with the output array.
+ */
+void	gsl_power2_fftac (const unsigned int n_values,
+			  const double      *ri_values_in,
+			  double            *ri_values_out);
+
+/**
+ * gsl_power2_fftsc
+ * @n_values:      Number of complex values
+ * @ri_values_in:  Complex frequency values [0..n_values*2-1]
+ * @ri_values_out: Complex sample values [0..n_values*2-1]
+ * This function performs a decimation in time fourier transformation
+ * in backwards direction with normalization. As such, this function
+ * represents the counterpart to gsl_power2_fftac(), that is, a value
+ * array which is transformed into the frequency domain with
+ * gsl_power2_fftac() can be reconstructed by issuing gsl_power2_fftsc()
+ * on the transform.
+ * Note that the transformation is performed out of place, the input
+ * array is not modified, and may not overlap with the output array.
+ */
+void	gsl_power2_fftsc (const unsigned int n_values,
+			  const double      *ri_values_in,
+			  double            *ri_values_out);
+
+/**
+ * gsl_power2_fftar
+ * @n_values:      Number of complex values
+ * @r_values_in:   Real sample values [0..n_values-1]
+ * @ri_values_out: Complex frequency values [0..n_values-1]
+ * Real valued variant of gsl_power2_fftac(), the input array contains
+ * real valued equidistant sampled data [0..n_values-1], and the output
+ * array contains the positive frequency half of the complex valued
+ * fourier transform. Note, that the complex valued fourier transform H
+ * of a purely real valued set of data, satisfies H(-f) = Conj(H(f)),
+ * where Conj() denotes the complex conjugate, so that just the positive
+ * frequency half suffices to describe the entire frequency spectrum.
+ * Even so, the resulting n_values/2 complex frequencies are one value
+ * off in storage size, but the resulting frequencies H(0) and
+ * H(n_values/2) are both real valued, so the real portion of
+ * H(n_values/2) is stored in ri_values_out[1] (the imaginery part of
+ * H(0)), so that both r_values_in and ri_values_out can be of size
+ * n_values.
+ * Note that the transformation is performed out of place, the input
+ * array is not modified, and may not overlap with the output array.
+ */
+void	gsl_power2_fftar (const unsigned int n_values,
+			  const double      *r_values_in,
+			  double            *ri_values_out);
+
+/**
+ * gsl_power2_fftsr
+ * @n_values:     Number of complex values
+ * @ri_values_in: Complex frequency values [0..n_values-1]
+ * @r_values_out: Real sample values [0..n_values-1]
+ * Real valued variant of gsl_power2_fftsc(), counterpart to
+ * gsl_power2_fftar(), using the same frequency storage format.
+ * A real valued data set transformed into the frequency domain
+ * with gsl_power2_fftar() can be reconstructed using this function.
+ * Note that the transformation is performed out of place, the input
+ * array is not modified, and may not overlap with the output array.
+ */
+void	gsl_power2_fftsr (const unsigned int n_values,
+			  const double      *ri_values_in,
+			  double            *r_values_out);
+
+
+/* --- convenience wrappers --- */
+void	gsl_power2_fftar_simple	(const unsigned int n_values,
+				 const float       *real_values,
+				 float		   *complex_values);
+void	gsl_power2_fftsr_simple	(const unsigned int n_values,
+				 const float	   *complex_values,
+				 float             *real_values);
+     
+     
+     
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* __GSL_FFT_H__ */   /* vim:set ts=8 sw=2 sts=2: */