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

       random, srandom, initstate, setstate - random number generator

       #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

       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 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	start‐
       ing  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().

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

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

       4.3BSD, POSIX.1-2001.

       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 near‐
       est 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 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,

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

       This  page  is  part of release 3.22 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2009-02-03			     RANDOM(3)

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