lrand48(3) — Linux manual page


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

NAME         top

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

SYNOPSIS         top

       #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: _XOPEN_SOURCE
           || /* Glibc since 2.19: */ _DEFAULT_SOURCE
           || /* Glibc versions <= 2.19: */ _SVID_SOURCE

DESCRIPTION         top

       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 over the
       interval [0.0, 1.0).

       The lrand48() and nrand48() functions return nonnegative long
       integers uniformly distributed over the interval [0, 2^31).

       The mrand48() and jrand48() functions return signed long integers
       uniformly distributed over the interval [-2^31, 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

       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 stor‐
       age 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 arbi‐
       trary 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 ini‐
       tial 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.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface             Attribute     Value                  │
       │drand48(), erand48(), │ Thread safety │ MT-Unsafe race:drand48 │
       │lrand48(), nrand48(), │               │                        │
       │mrand48(), jrand48(), │               │                        │
       │srand48(), seed48(),  │               │                        │
       │lcong48()             │               │                        │
       The above functions record global state information  for  the  random
       number generator, so they are not thread-safe.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4.

SEE ALSO         top

       rand(3), random(3)

COLOPHON         top

       This page is part of release 5.08 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

                                 2017-09-15                       DRAND48(3)