random


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 init-
       state() 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.  The setstate() function returns
       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().

CONFORMING TO
       The Art of Scientific Computing (William H. Press, Brian  P.  Flannery,
       Saul  A.  Teukolsky, William T. Vetterling; New York: Cambridge Univer-
       sity Press, 2007, 3rd ed.)  provides an excellent discussion of practi-
       cal 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.

SEE ALSO
       drand48(3), rand(3), random_r(3), srand(3)

COLOPHON
       This  page  is  part of release 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.



GNU                               2010-09-20                         RANDOM(3)
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