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/*
* Copyright (C) 2005 Guochun Shi <gshi@ncsa.uiuc.edu>
* Copyright (C) 2005 International Business Machines Inc.
*
* 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 2.1 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., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <stdlib.h>
/* Intended usage is srand(cl_randseed()).
* This returns on "as good as it gets" random number usually taken from
* /dev/urandom to have a nice seed for future random numbers generated by
* rand(). */
unsigned int cl_randseed(void);
/* get_next_random() currently rand() based.
*
* You probably want to use cl_rand_from_interval instead.
*
* You don't need to srand(), it will seed once with cl_randseed internally.
*
* It is called that way, because it was exposed in the header file for a long
* time, and used to be coded in an attempt to pregenerate a queue of random
* numbers from the mainloop, and it would shift the next random number from
* that queue and trigger generation of new random numbers "at idle time" to
* refill that queue.
* Only that functionality never actually worked, is not interessting anymore
* anyways (rand() is cheap enough), and is now ripped out.
*
* So it now does srand(cl_randseed()) once internally,
* and from there on is equivalent to calling rand() directly,
* and could be called cl_rand().
*
* If you want your own specific rand seed to re-generate a particular
* sequence, call it once, throw away the return code, then call
* srand(yourseed). Or don't use it anywhere in your code. */
int get_next_random(void);
/* generate some random number in the range [a;b];
* typically used to randomly delay messages. */
#define HAVE_CL_RAND_FROM_INTERVAL 1
static inline
int cl_rand_from_interval(const int a, const int b)
{
/*
* Be careful here, you don't know RAND_MAX at coding time,
* only at compile time. If you think
* (int)(a + (rand()*(b-a)+(RAND_MAX/2))/RAND_MAX);
* was correct, think again with RAND_MAX = INT_MAX,
* which is the case for many rand() implementations nowadays.
*
* Don't do modulo, either, as that will skew the distribution, and
* still has possible wraparounds, or an insufficient input set for too
* small RAND_MAX.
*
* Rather do the whole calculation in 64 bit, which should be correct
* as long as r, a, b, and RAND_MAX are all int.
* Of course, if you prefer, you can do it with floating point as well.
*/
#if 1 /* use long long */
long long r = get_next_random();
r = a + (r * (b-a) + RAND_MAX/2)/RAND_MAX;
#else /* use floating point */
int r = get_next_random();
r = a + (int)(1.0 / RAND_MAX * r * (b-a) + 0.5);
#endif
return r;
}
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