NAME

       initstate, random, setstate, srandom - pseudo-random number functions

SYNOPSIS

       #include <stdlib.h>

       char *initstate(unsigned seed, char *state, size_t size);
       long random(void);
       char *setstate(const char *state);
       void srandom(unsigned seed);

DESCRIPTION

       The  random()  function  shall  use  a  non-linear  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
       shall increase the period.

       With 256 bytes of state information, the period of the random-number  generator  shall  be  greater  than
       2**69.

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

       The srandom() function shall initialize the current state array using the value of 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, shall be used by
       initstate() to decide what type of random-number generator 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 nearest one of these values. If initstate() is called
       with 8<=size<32, then random() shall use 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 shall return a pointer to the previous state information array.

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

       Once a state has been initialized, setstate() allows switching between state arrays. The array defined by
       the state argument shall be used for further random-number generation  until  initstate()  is  called  or
       setstate() is called again. The setstate() function shall return a pointer to the previous state array.

RETURN VALUE

       If initstate() is called with size less than 8, it shall return NULL.

       The random() function shall return the generated pseudo-random number.

       The srandom() function shall not return a value.

       Upon  successful  completion,  initstate()  and  setstate()  shall return a pointer to the previous state
       array; otherwise, a null pointer shall be returned.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

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

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

        2. 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 initialized.

       Although some implementations of random() have written messages to standard error,  such  implementations
       do not conform to IEEE Std 1003.1-2001.

       Issue 5 restored the historical behavior of this function.

       Threaded  applications  should  use  erand48(),  nrand48(),  or  jrand48()  instead  of  random() when an
       independent random number sequence in multiple threads is required.

RATIONALE

       None.

FUTURE DIRECTIONS

       None.

SEE ALSO

       drand48() , rand() , the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>

COPYRIGHT

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition,
       Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open  Group  Base
       Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers,
       Inc  and  The  Open Group. In the event of any discrepancy between this version and the original IEEE and
       The Open Group Standard, the original IEEE and The Open Group  Standard  is  the  referee  document.  The
       original Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group                                   2003                                          INITSTATE(P)