This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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 POSIX.1‐2008.

       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.

       These  functions  should  be  avoided  whenever  non-trivial  requirements  (including safety) have to be
       fulfilled.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group  Base
       Specifications  Issue  7, 2018 Edition, Copyright (C) 2018 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 .

       Any  typographical  or formatting errors that appear in this page are most likely to have been introduced
       during  the  conversion  of  the  source  files  to  man  page  format.  To  report  such   errors,   see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                     INITSTATE(3POSIX)

       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 231-1. The period of this random-number generator is approximately 16 x (231-1).  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 269.

       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.

       No errors are defined.

       Thefollowingsectionsareinformative.

       None.

       None.

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

       This  manual  page  is part of the POSIX Programmer's Manual.  The Linux implementation of this interface
       may differ (consult the corresponding Linux manual page for details of Linux behavior), or the  interface
       may not be implemented on Linux.

       None.

       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.

drand48(), rand()

       The Base Definitions volume of POSIX.1‐2017, <stdlib.h>

       #include <stdlib.h>

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