rand(3C)							      rand(3C)

NAME    [Toc]    [Back]

     rand, srand, rand_r - simple random-number	generator

SYNOPSIS    [Toc]    [Back]

     #include <stdlib.h>

     int rand (void);

     int rand_r	(unsigned int *seed);

     void srand	(unsigned int seed);

DESCRIPTION    [Toc]    [Back]

     rand uses a multiplicative	congruent random-number	generator with period
     2^32 that returns successive pseudo-random	numbers	in the range from 0 to
     (2^15)-1.

     The function srand	uses the argument seed as a seed for a new sequence of
     pseudo-random numbers to be returned by subsequent	calls to the function
     rand.  If the function srand is then called with the same seed value, the
     sequence of pseudo-random numbers will be repeated.  If the function rand
     is	called before any calls	to srand have been made, the same sequence
     will be generated as when srand is	first called with a seed value of 1.

     rand_r is a reentrant version of rand.  If	rand_r is called with the same
     initial value for *seed and the value of *seed is not changed between
     successive	returns	and calls to rand_r, the same sequence shall be
     generated.	 This function is useful when multiple threads in a process
     each wish to get their own	repeatable pseudo-random number	sequence.  The
     feature test macro	_SGI_REENTRANT_FUNCTIONS should	be defined to make
     this function visible.

NOTES    [Toc]    [Back]

     The spectral properties of	rand are limited.  drand48(3C) and random(3B)
     provide a much better, though more	elaborate, random-number generator.

     In	a multi-threaded program rand is made MP safe by single-threading
     access to the shared seed.	 For best performance threaded applications
     should use	rand_r instead.

SEE ALSO    [Toc]    [Back]

     drand48(3C), random(3B)


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