poisson.cc

来自「早期freebsd实现」· CC 代码 · 共 37 行

/* 
Copyright (C) 1988 Free Software Foundation
    written by Dirk Grunwald ([e-mail])

This file is part of the GNU C++ Library.  This library is free
software; you can redistribute it and/or modify it under the terms of
the GNU Library 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 Library General Public License for more details.
You should have received a copy of the GNU Library General Public
License along with this library; if not, write to the Free Software
Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
*/
#ifdef __GNUG__
#pragma implementation
#endif
#include <builtin.h>
#include <Random.h>
#include <Poisson.h>

double Poisson::operator()()
{
    double bound = exp(-1.0 * pMean);
    int count = 0;

    for (double product = 1.0;
	 product >= bound;
	 product *= pGenerator -> asDouble()) {
	     count++;
	 }
    return(count - 1);
}