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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 06:40:13 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-17 06:40:13 +0000 |
commit | e9be59e1502a41bab9891d96d753102a7dafef0b (patch) | |
tree | c3b2da87c414881f4b53d0964f407c83492d813e /include/clplumbing/cl_random.h | |
parent | Initial commit. (diff) | |
download | cluster-glue-e9be59e1502a41bab9891d96d753102a7dafef0b.tar.xz cluster-glue-e9be59e1502a41bab9891d96d753102a7dafef0b.zip |
Adding upstream version 1.0.12.upstream/1.0.12upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'include/clplumbing/cl_random.h')
-rw-r--r-- | include/clplumbing/cl_random.h | 81 |
1 files changed, 81 insertions, 0 deletions
diff --git a/include/clplumbing/cl_random.h b/include/clplumbing/cl_random.h new file mode 100644 index 0000000..d1e37ce --- /dev/null +++ b/include/clplumbing/cl_random.h @@ -0,0 +1,81 @@ + +/* + * 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; +} |