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);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       random(), srandom(), initstate(), setstate():
           _SVID_SOURCE || _BSD_SOURCE || _XOPEN_SOURCE >= 500 || _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

DESCRIPTION

       The  random()  function  uses  a  nonlinear 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
       RAND_MAX.  The period of this random number generator 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 random() 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 initstate() 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() function returns no value.

       The  initstate()  function  returns  a  pointer  to  the previous state array.  On error, errno is set to
       indicate the cause.

       On success, setstate() returns a pointer to the previous state array.  On error, it  returns  NULL,  with
       errno set to indicate the cause of the error.

ERRORS

       EINVAL The state argument given to setstate() was NULL.

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

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────┬───────────────┬─────────┐
       │Interface               │ Attribute     │ Value   │
       ├────────────────────────┼───────────────┼─────────┤
       │random(), srandom(),    │ Thread safety │ MT-Safe │
       │initstate(), setstate() │               │         │
       └────────────────────────┴───────────────┴─────────┘

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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.

       This function should not be used in cases where multiple threads use random() and the behavior should  be
       reproducible.  Use random_r(3) for that purpose.

       Random-number  generation  is  a  complex topic.  Numerical Recipes in C: The Art of Scientific Computing
       (William H. Press, Brian P. Flannery, Saul A. Teukolsky,  William  T.  Vetterling;  New  York:  Cambridge
       University  Press, 2007, 3rd ed.)  provides an excellent discussion of practical random-number generation
       issues in Chapter 7 (Random Numbers).

       For a more theoretical discussion which also covers many practical issues in depth, see Chapter 3 (Random
       Numbers)  in  Donald E. Knuth's The Art of Computer Programming, volume 2 (Seminumerical Algorithms), 2nd
       ed.; Reading, Massachusetts: Addison-Wesley Publishing Company, 1981.

BUGS

       According to POSIX, initstate() should return NULL on error.  In the glibc implementation, errno  is  (as
       specified) set on error, but the function does not return NULL.

SEE ALSO

       drand48(3), getrandom(2), rand(3), random_r(3), srand(3)

COLOPHON

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