INITSTATE(3)               POSIX Programmer's Manual              INITSTATE(3)



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


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

SSYYNNOOPPSSIISS
       #include <stdlib.h>

       char *initstate(unsigned _s_e_e_d, char *_s_t_a_t_e, size_t _s_i_z_e);
       long random(void);
       char *setstate(char *_s_t_a_t_e);
       void srandom(unsigned _s_e_e_d);

DDEESSCCRRIIPPTTIIOONN
       The _r_a_n_d_o_m() function shall use a non-linear additive feedback random-
       number generator employing a default state array size of 31 lloonngg
       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 _r_a_n_d(), _r_a_n_d_o_m() shall produce by default a sequence of numbers
       that can be duplicated by calling _s_r_a_n_d_o_m() with 1 as the seed.

       The _s_r_a_n_d_o_m() function shall initialize the current state array using
       the value of _s_e_e_d.

       The _i_n_i_t_s_t_a_t_e() and _s_e_t_s_t_a_t_e() functions handle restarting and changing
       random-number generators. The _i_n_i_t_s_t_a_t_e() function allows a state
       array, pointed to by the _s_t_a_t_e argument, to be initialized for future
       use. The _s_i_z_e argument, which specifies the size in bytes of the state
       array, shall be used by _i_n_i_t_s_t_a_t_e() 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 _i_n_i_t_s_t_a_t_e() is called with
       8<=_s_i_z_e<32, then _r_a_n_d_o_m() shall use a simple linear congruential random
       number generator. The _s_e_e_d argument specifies a starting point for the
       random-number sequence and provides for restarting at the same point.
       The _i_n_i_t_s_t_a_t_e() function shall return a pointer to the previous state
       information array.

       If _i_n_i_t_s_t_a_t_e() has not been called, then _r_a_n_d_o_m() shall behave as
       though _i_n_i_t_s_t_a_t_e() had been called with _s_e_e_d=1 and _s_i_z_e=128.

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

RREETTUURRNN VVAALLUUEE
       If _i_n_i_t_s_t_a_t_e() is called with _s_i_z_e less than 8, it shall return NULL.

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

       The _s_r_a_n_d_o_m() function shall not return a value.

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

EERRRROORRSS
       No errors are defined.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
       None.

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

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

        2. The _s_e_t_s_t_a_t_e() function, with the desired state, can be used,
           followed by _s_r_a_n_d_o_m() 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 _r_a_n_d_o_m() 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 _e_r_a_n_d_4_8(), _n_r_a_n_d_4_8(), or _j_r_a_n_d_4_8()
       instead of _r_a_n_d_o_m() when an independent random number sequence in
       multiple threads is required.

RRAATTIIOONNAALLEE
       None.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       None.

SSEEEE AALLSSOO
       _d_r_a_n_d_4_8(), _r_a_n_d()

       The Base Definitions volume of POSIX.1-2008, <<ssttddlliibb..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
       -- Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, Copyright (C) 2013 by the Institute of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is
       POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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                  2013                         INITSTATE(3)
