DRAND48(3)                                          Linux Programmer's Manual                                         DRAND48(3)



NAME
       drand48,  erand48,  lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48 - generate uniformly distributed pseudo-
       random numbers

SYNOPSIS
       #include <stdlib.h>

       double drand48(void);

       double erand48(unsigned short xsubi[3]);

       long int lrand48(void);

       long int nrand48(unsigned short xsubi[3]);

       long int mrand48(void);

       long int jrand48(unsigned short xsubi[3]);

       void srand48(long int seedval);

       unsigned short *seed48(unsigned short seed16v[3]);

       void lcong48(unsigned short param[7]);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       All functions shown above: _SVID_SOURCE || _XOPEN_SOURCE

DESCRIPTION
       These functions generate pseudo-random numbers using the linear congruential algorithm and 48-bit integer arithmetic.

       The drand48() and erand48() functions return nonnegative double-precision  floating-point  values  uniformly  distributed
       between [0.0, 1.0).

       The lrand48() and nrand48() functions return nonnegative long integers uniformly distributed between 0 and 2^31.

       The mrand48() and jrand48() functions return signed long integers uniformly distributed between -2^31 and 2^31.

       The  srand48(), seed48() and lcong48() functions are initialization functions, one of which should be called before using
       drand48(), lrand48() or mrand48().  The functions erand48(), nrand48() and jrand48() do  not  require  an  initialization
       function to be called first.

       All the functions work by generating a sequence of 48-bit integers, Xi, according to the linear congruential formula:

              Xn+1 = (aXn + c) mod m, where n >= 0

       The parameter m = 2^48, hence 48-bit integer arithmetic is performed.  Unless lcong48() is called, a and c are given by:

              a = 0x5DEECE66D
              c = 0xB

       The value returned by any of the functions drand48(), erand48(), lrand48(), nrand48(), mrand48() or jrand48() is computed
       by first generating the next 48-bit Xi in the sequence.  Then the appropriate number of bits, according to  the  type  of
       data item to be returned, is copied from the high-order bits of Xi and transformed into the returned value.

       The functions drand48(), lrand48() and mrand48() store the last 48-bit Xi generated in an internal buffer.  The functions
       erand48(), nrand48() and jrand48() require the calling program to provide storage for the successive  Xi  values  in  the
       array argument xsubi.  The functions are initialized by placing the initial value of Xi into the array before calling the
       function for the first time.

       The initializer function srand48() sets the high order 32-bits of Xi to the argument seedval.  The low order 16-bits  are
       set to the arbitrary value 0x330E.

       The  initializer function seed48() sets the value of Xi to the 48-bit value specified in the array argument seed16v.  The
       previous value of Xi is copied into an internal buffer and a pointer to this buffer is returned by seed48().

       The initialization function lcong48() allows the user to specify initial values for Xi, a and c.  Array argument elements
       param[0-2]  specify  Xi,  param[3-5]  specify a, and param[6] specifies c.  After lcong48() has been called, a subsequent
       call to either srand48() or seed48() will restore the standard values of a and c.

CONFORMING TO
       SVr4, POSIX.1-2001.

NOTES
       These functions are declared obsolete by SVID 3, which states that rand(3) should be used instead.

SEE ALSO
       rand(3), random(3)

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           2007-07-26                                                 DRAND48(3)