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random(3C)		 Standard C Library Functions		    random(3C)

       random, srandom,	initstate, setstate - pseudorandom number functions

       #include	<stdlib.h>

       long random(void);

       void srandom(unsigned int seed);

       char *initstate(unsigned	int seed, char *state, size_t size);

       char *setstate(const char *state);

       The  random() function uses a nonlinear additive	feedback random-number
       generator employing a default state array size of 31 long  integers  to
       return  successive  pseudo-random  numbers in the range from 0 to 2**31
       -1. The period of this random-number generator is approximately 16 x (2
      **31  -1). The size of the state array determines	the period of the ran-
       dom-number generator. Increasing	the state  array  size	increases  the

       The  srandom()  function	 initializes the current state array using the
       value of	seed.

       The random() and	srandom() functions have  (almost)  the	 same  calling
       sequence	 and  initialization  properties  as  rand()  and srand() (see
       rand(3C)). The difference is that rand(3C) produces a much less	random
       sequence--in  fact,  the	 low dozen bits	generated by rand go through a
       cyclic pattern. All the bits generated by random() are usable.

       The algorithm from rand() is used by srandom() to generate the 31 state
       integers.  Because  of  this,  different	srandom() seeds	often produce,
       within an offset, the same sequence of low order	bits from random(). If
       low  order  bits	are used directly, random() should be initialized with
       setstate() using	high quality random values.

       Unlike srand(), srandom() does not return  the  old  seed  because  the
       amount  of  state information used is much more than a single word. Two
       other routines are provided to  deal  with  restarting/changing	random
       number  generators.  With 256 bytes of state information, the period of
       the random-number generator is greater than 2**69, which	should be suf-
       ficient for most	purposes.

       Like  rand(3C), random()	produces by default a sequence of numbers that
       can be duplicated by calling srandom() with 1 as	the seed.

       The initstate() and setstate() functions	handle restarting and changing
       random-number  generators.   The	 initstate()  function	allows a state
       array, pointed to by the	state argument,	to be initialized  for	future
       use.  The size argument,	which specifies	the size in bytes of the state
       array, is used by initstate() to	decide what type of random-number gen-
       erator to use; the larger the state array, the more random the numbers.
       Values for the amount of	state information are 8, 32, 64, 128, and  256
       bytes.  Other values greater than 8 bytes are rounded down to the near-
       est one of these	values.	 For values smaller than 8,  random()  uses  a
       simple  linear congruential random number generator.  The seed argument
       specifies a starting point for the random-number	sequence and  provides
       for  restarting	at the same point.  The	initstate() function returns a
       pointer to the previous state information array.

       If initstate() has not been called, then	 random()  behaves  as	though
       initstate() had been called with	seed=1 and size=128.

       If  initstate() is called with size<8, then random() uses a simple lin-
       ear congruential	random number generator.

       Once a state has	been initialized, setstate() allows switching  between
       state  arrays. The array	defined	by the state argument is used for fur-
       ther random-number generation until initstate() is called or setstate()
       is  called again. The setstate()	function returns a pointer to the pre-
       vious state array.

       The random() function returns the generated pseudo-random number.

       The srandom() function returns no value.

       Upon successful completion, initstate() and setstate() return a pointer
       to the previous state array.  Otherwise,	a null pointer is returned.

       No errors are defined.

       After  initialization,  a  state	 array can be restarted	at a different
       point in	one of two ways:

	 o  The	initstate() function can be used, with the desired seed, state
	    array, and size of the array.

	 o  The	setstate() function, with the desired state, can be used, fol-
	    lowed by srandom() with the	desired	seed. The advantage  of	 using
	    both  of  these functions is that the size of the state array does
	    not	have to	be saved once it is initialized.

       Example 1: Initialize an	array.

       The following example demonstrates the use of initstate() to  intialize
       an  array.  It also demonstrates	how to initialize an array and pass it
       to setstate().

       # include <stdlib.h>
       static unsigned int state0[32];
       static unsigned int state1[32] =	{
	    0x9a319039,	0x32d9c024, 0x9b663182,	0x5da1f342,
	    0x7449e56b,	0xbeb1dbb0, 0xab5c5918,	0x946554fd,
	    0x8c2e680f,	0xeb3d799f, 0xb11ee0b7,	0x2d436b86,
	    0xda672e2a,	0x1588ca88, 0xe369735d,	0x904f35f7,
	    0xd7158fd6,	0x6fa6f051, 0x616e6b96,	0xac94efdc,
	    0xde3b81e0,	0xdf0a6fb5, 0xf103bc02,	0x48f340fb,
	    0x36413f93,	0xc622c298, 0xf5a42ab8,	0x8a88d77b,
	    0xf5ad9d0e,	0x8999220b, 0x27fb47b9
       main() {
	    unsigned seed;
	    int	n;
	    seed = 1;
	    n =	128;
	    (void)initstate(seed, (char	*)state0, n);
	    printf("random() = %d0\n", random());
	    (void)setstate((char *)state1);
	    printf("random() = %d0\n", random());

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE	TYPE	     |	    ATTRIBUTE VALUE	   |
       |Interface Stability	     |Standard			   |
       |MT-Level		     |See NOTES	below.		   |

       drand48(3C), rand(3C), attributes(5), standards(5)

       The random() and	srandom() functions are	unsafe in multithreaded	appli-

       Use of these functions in multithreaded applications is unsupported.

       For  initstate()	 and setstate(), the state argument must be aligned on
       an int boundary.

       Newer and better	performing random number generators such as  addrans()
       and lcrans() are	available with the SUNWspro package.

SunOS 5.10			  14 Aug 2002			    random(3C)


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