initstate man page on SunOS

Man page or keyword search:  
man Server   20652 pages
apropos Keyword Search (all sections)
Output format
SunOS logo
[printable version]

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 ran‐
       dom-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:

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

	 ·  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.

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	     │Standard			   │
       ├─────────────────────────────┼─────────────────────────────┤
       │MT-Level		     │See NOTES below.		   │
       └─────────────────────────────┴─────────────────────────────┘

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 5.10			  14 Aug 2002			    random(3C)
[top]

List of man pages available for SunOS

Copyright (c) for man pages and the logo by the respective OS vendor.

For those who want to learn more, the polarhome community provides shell access and support.

[legal] [privacy] [GNU] [policy] [cookies] [netiquette] [sponsors] [FAQ]
Tweet
Polarhome, production since 1999.
Member of Polarhome portal.
Based on Fawad Halim's script.
....................................................................
Vote for polarhome
Free Shell Accounts :: the biggest list on the net