/usr/include/fht.h is in libalglib-dev 2.6.0-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Copyright (c) 2009, Sergey Bochkanov (ALGLIB project).
>>> SOURCE LICENSE >>>
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation (www.fsf.org); either version 2 of the
License, or (at your option) any later version.
This program 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 General Public License for more details.
A copy of the GNU General Public License is available at
http://www.fsf.org/licensing/licenses
>>> END OF LICENSE >>>
*************************************************************************/
#ifndef _fht_h
#define _fht_h
#include "ap.h"
#include "ialglib.h"
#include "ftbase.h"
#include "fft.h"
/*************************************************************************
1-dimensional Fast Hartley Transform.
Algorithm has O(N*logN) complexity for any N (composite or prime).
INPUT PARAMETERS
A - array[0..N-1] - real function to be transformed
N - problem size
OUTPUT PARAMETERS
A - FHT of a input array, array[0..N-1],
A_out[k] = sum(A_in[j]*(cos(2*pi*j*k/N)+sin(2*pi*j*k/N)), j=0..N-1)
-- ALGLIB --
Copyright 04.06.2009 by Bochkanov Sergey
*************************************************************************/
void fhtr1d(ap::real_1d_array& a, int n);
/*************************************************************************
1-dimensional inverse FHT.
Algorithm has O(N*logN) complexity for any N (composite or prime).
INPUT PARAMETERS
A - array[0..N-1] - complex array to be transformed
N - problem size
OUTPUT PARAMETERS
A - inverse FHT of a input array, array[0..N-1]
-- ALGLIB --
Copyright 29.05.2009 by Bochkanov Sergey
*************************************************************************/
void fhtr1dinv(ap::real_1d_array& a, int n);
#endif
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