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

NAME
       random, srandom, initstate, setstate - pseudorandom number functions

SYNOPSIS
       #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);

DESCRIPTION
       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 random-
       number generator. Increasing the state array size increases the period.

       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.

RETURN VALUES
       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.

ERRORS
       No errors are defined.

USAGE
       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,	 followed  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 ini‐
		  tialized.

EXAMPLES
       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] = {
	      3,
	      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());
	 }

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

       ┌─────────────────────────────┬─────────────────────────────┐
       │      ATTRIBUTE TYPE	     │	    ATTRIBUTE VALUE	   │
       ├─────────────────────────────┼─────────────────────────────┤
       │Interface Stability	     │Committed			   │
       ├─────────────────────────────┼─────────────────────────────┤
       │MT-Level		     │See NOTES below.		   │
       ├─────────────────────────────┼─────────────────────────────┤
       │Standard		     │See standards(5).		   │
       └─────────────────────────────┴─────────────────────────────┘

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

NOTES
       The random() and srandom() functions are unsafe in multithreaded appli‐
       cations.

       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 5.11			  14 Aug 2002			    random(3C)
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