icon Top 9 categories map      RocketAware > man pages >


Tips: Browse or Search all pages for efficient awareness of more than 6000 of the most popular reusable and open source applications, functions, libraries, and FAQs.

The "RKT couplings" below include links to source code, updates, additional information, advice, FAQs, and overviews.


Search all pages


By activity
Professions, Sciences, Humanities, Business, ...

User Interface
Text-based, GUI, Audio, Video, Keyboards, Mouse, Images,...

Text Strings
Conversions, tests, processing, manipulation,...

Integer, Floating point, Matrix, Statistics, Boolean, ...

Algorithms, Memory, Process control, Debugging, ...

Stored Data
Data storage, Integrity, Encryption, Compression, ...

Networks, protocols, Interprocess, Remote, Client Server, ...

Hard World
Timing, Calendar and Clock, Audio, Video, Printer, Controls...

File System
Management, Filtering, File & Directory access, Viewers, ...


RocketLink!--> Man page versions: OpenBSD FreeBSD RedHat Solaris Others

RANDOM(3)                 OpenBSD Programmer's Manual                RANDOM(3)

     random, srandom, initstate, setstate - better random number generator;
     routines for changing generators

     #include <stdlib.h>


     srandom(unsigned int seed);

     char *
     initstate(unsigned int seed, char *state, size_t n);

     char *
     setstate(const char *state);

     The random() function uses a non-linear additive feedback random number
     generator employing a default table of size 31 long integers to return
     successive pseudo-random numbers in the range from 0 to (2**31)-1.  The
     maximum value returned by random() is LONG_MAX (as defined by the header
     file <limits.h>). The period of this random number generator is very
     large, approximately 16*((2**31)-1.

     The random()/ srandom() have (almost) the same calling sequence and ini-
     tialization properties as rand(3)/ srand(3).   The difference is that
     rand produces a much less random sequence -- in fact, the low dozen bits
     generated by rand go through a cyclic pattern.  All the bits generated by
     random() are usable.  For example, `random()&01' will produce a random
     binary value.

     Unlike srand,  srandom() does not return the old seed; the reason for
     this is that the amount of state information used is much more than a
     single word.  (Two other routines are provided to deal with restart-
     ing/changing random number generators).  Like rand(3),  however, random()
     will by default produce a sequence of numbers that can be duplicated by
     calling srandom() with `1' as the seed.

     The initstate() routine allows a state array, passed in as an argument,
     to be initialized for future use.  The size of the state array (in bytes)
     is used by initstate() to decide how sophisticated a random number gener-
     ator it should use -- the more state, the better the random numbers will
     be.  (Current "optimal" values for the amount of state information are 8,
     32, 64, 128, and 256 bytes; other amounts will be rounded down to the
     nearest known amount.  Using less than 8 bytes will cause an error.)  The
     seed for the initialization (which specifies a starting point for the
     random number sequence, and provides for restarting at the same point) is
     also an argument.  The initstate() function returns a pointer to the pre-
     vious state information array.

     Once a state has been initialized, the setstate() routine provides for
     rapid switching between states.  The setstate() function returns a point-
     er to the previous state array; its argument state array is used for fur-
     ther random number generation until the next call to initstate() or

     Once a state array has been initialized, it may be restarted at a differ-
     ent point either by calling initstate() (with the desired seed, the state
     array, and its size) or by calling both setstate() (with the state array)
     and srandom() (with the desired seed).  The advantage of calling both
     setstate() and srandom() is that the size of the state array does not
     have to be remembered after it is initialized.

     With 256 bytes of state information, the period of the random number gen-
     erator is greater than 2**69 which should be sufficient for most purpos-

     Earl T. Cohen

     If initstate() is called with less than 8 bytes of state information, or
     if setstate() detects that the state information has been garbled, error
     messages are printed on the standard error output.

     arc4random(3),  drand48(3),  rand(3)

     The random(), srandom(), initstate(), and setstate() functions conform to
     X/Open Portability Guide Issue 4.2 (``XPG4.2'').

     These functions appeared in 4.2BSD.

     About 2/3 the speed of rand(3).

OpenBSD 2.6                     April 19, 1991                               2

Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.

(Corrections, notes, and links courtesy of RocketAware.com)

[Detailed Topics]
FreeBSD Sources for random(3) functions
OpenBSD sources for random(3)

[Overview Topics]

Up to: Random Numbers

RocketLink!--> Man page versions: OpenBSD FreeBSD RedHat Solaris Others

Rapid-Links: Search | About | Comments | Submit Path: RocketAware > man pages > random.3/
RocketAware.com is a service of Mib Software
Copyright 1999, Forrest J. Cavalier III. All Rights Reserved.
We welcome submissions and comments