random - phpMan

RANDOM(3)                  Linux Programmer’s Manual                 RANDOM(3)



NAME
       random, srandom, initstate, setstate - random number generator

SYNOPSIS
       #include <stdlib.h>

       long int random(void);
       void srandom(unsigned int seed);
       char *initstate(unsigned int seed, char *state, size_t n);
       char *setstate(char *state);

DESCRIPTION
       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-ran-
       dom numbers in the range from 0 to RAND_MAX.  The period of this random number gen-
       erator is very large, approximately 16*((2**31)-1).

       The srandom() function sets its argument as the seed for a new sequence of  pseudo-
       random  integers  to  be  returned  by random().  These sequences are repeatable by
       calling srandom() with the same seed value.  If no seed value is provided, the ran-
       dom() function is automatically seeded with a value of 1.

       The  initstate()  function  allows a state array state to be initialized for use by
       random().  The size of the state array n is  used  by  initstate()  to  decide  how
       sophisticated a random number generator it should use — the larger the state array,
       the better the random numbers will be.  seed is the seed  for  the  initialization,
       which  specifies  a starting point for the random number sequence, and provides for
       restarting at the same point.

       The setstate() function changes the state array used by the random() function.  The
       state array state is used for random number generation until the next call to init-
       state() or setstate().  state must first have been initialized using initstate() or
       be the result of a previous call of setstate().

RETURN VALUE
       The  random() function returns a value between 0 and RAND_MAX.  The srandom() func-
       tion returns no value.  The initstate() and setstate() functions return  a  pointer
       to the previous state array, or NULL on error.

ERRORS
       EINVAL A state array of less than 8 bytes was specified to initstate().

NOTES
       Current  "optimal" values for the size of the state array n 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.

CONFORMING TO
       BSD 4.3

SEE ALSO
       rand(3), srand(3)



GNU                               2000-08-20                         RANDOM(3)

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