prepare simple Fortran interface

pocketfft/pocketfft.h

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+/*
+ * This file is part of pocketfft.
+ * Licensed under a 3-clause BSD style license - see LICENSE.md
+ */
+
+/*! \file pocketfft.h
+ *  Public interface of the pocketfft library
+ *
+ *  Copyright (C) 2008-2019 Max-Planck-Society
+ *  \author Martin Reinecke
+ */
+
+#ifndef POCKETFFT_H
+#define POCKETFFT_H
+
+#include <stdlib.h>
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+struct pocketfft_plan_c_i;
+typedef struct pocketfft_plan_c_i * pocketfft_plan_c;
+pocketfft_plan_c pocketfft_make_plan_c (size_t length);
+void pocketfft_delete_plan_c (pocketfft_plan_c plan);
+int pocketfft_backward_c(pocketfft_plan_c plan, double c[], double fct);
+int pocketfft_forward_c(pocketfft_plan_c plan, double c[], double fct);
+size_t pocketfft_length_c(pocketfft_plan_c plan);
+
+struct pocketfft_plan_r_i;
+typedef struct pocketfft_plan_r_i * pocketfft_plan_r;
+pocketfft_plan_r pocketfft_make_plan_r (size_t length);
+void pocketfft_delete_plan_r (pocketfft_plan_r plan);
+/*! Computes a real backward FFT on \a c, using \a plan
+    and assuming the FFTPACK storage scheme:
+    - on entry, \a c has the form <tt>r0, r1, i1, r2, i2, ...</tt>
+    - on exit, it has the form <tt>r0, r1, ..., r[length-1]</tt>. */
+int pocketfft_backward_r(pocketfft_plan_r plan, double c[], double fct);
+/*! Computes a real forward FFT on \a c, using \a plan
+    and assuming the FFTPACK storage scheme:
+    - on entry, \a c has the form <tt>r0, r1, ..., r[length-1]</tt>;
+    - on exit, it has the form <tt>r0, r1, i1, r2, i2, ...</tt> */
+int pocketfft_forward_r(pocketfft_plan_r plan, double c[], double fct);
+size_t pocketfft_length_r(pocketfft_plan_r plan);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif