randomSeed.hpp

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/** \file randomSeed.hpp
 * \author Jared R. Males
 * \brief Defines a random number seed generator
 * \ingroup gen_math_files
 *
 */
 
//***********************************************************************//
// Copyright 2015, 2016, 2017, 2020 Jared R. Males (jaredmales@gmail.com)
//
// This file is part of mxlib.
//
// mxlib 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, either version 3 of the License, or
// (at your option) any later version.
//
// mxlib 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.
//
// You should have received a copy of the GNU General Public License
// along with mxlib.  If not, see <http://www.gnu.org/licenses/>.
//***********************************************************************//
 
#ifndef mx_math_randomSeed_hpp
#define mx_math_randomSeed_hpp
 
#include <unistd.h>
#include <fcntl.h>
 
#include "../mxlib.hpp"
 
namespace mx
{
namespace math
{
 
/// Get a value to use as a random seed
/** On Linux systems, uses /dev/urandom to populate the value with sizeof(intT) bytes.
 * Otherwise, uses time(0) to get time since the epoch.
 *
 * \returns 0 on success.
 * \returns -1 on error.
 *
 * \tparam intT is the integer type of seeval.
 *
 * \ingroup random
 *
 */
template <typename intT>
int randomSeed( intT &seedval /**< [out] will be populated with the seed.*/ )
{
#ifdef __linux__
 
    int fd;
 
    errno = 0;
    fd = open( "/dev/urandom", O_RDONLY );
 
    if( fd < 0 )
    {
        internal::mxlib_error_report(errno2error_t(errno), "error opening /dev/urandom" );
 
        return -1;
    }
 
    seedval = 0;
 
    errno = 0;
    int rv = ::read( fd, &seedval, sizeof( intT ) );
 
    if( rv < 0 )
    {
        internal::mxlib_error_report(errno2error_t(errno), "Error on read from /dev/urandom." );
        close( fd );
        return -1;
    }
 
    close( fd );
 
    int sz = sizeof( intT );
 
    if( rv < sz )
    {
        internal::mxlib_error_report(error_t::filererr, "Read from /dev/urandom did not return enough bytes" );
 
        return -1;
    }
 
    return 0;
 
#endif //__linux__
 
    seedval = time( 0 );
 
    return 0;
}
 
} // namespace math
} // namespace mx
 
#endif // mx_math_randomSeed_hpp