DRAND48(3) Linux Programmer's Manual DRAND48(3)
NAME
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48,
lcong48  generate uniformly distributed pseudorandom 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 pseudorandom numbers using the linear congru
ential algorithm and 48bit integer arithmetic.
The drand48() and erand48() functions return nonnegative doublepreci
sion floatingpoint 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 uni
formly 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 48bit integers, Xi,
according to the linear congruential formula:
Xn+1 = (aXn + c) mod m, where n >>= 0
The parameter m = 2^48, hence 48bit 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 gen
erating the next 48bit Xi in the sequence. Then the appropriate num
ber of bits, according to the type of data item to be returned, is
copied from the highorder bits of Xi and transformed into the returned
value.
The functions drand48(), lrand48() and mrand48() store the last 48bit
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 32bits of Xi to
the argument seedval. The low order 16bits are set to the arbitrary
value 0x330E.
The initializer function seed48() sets the value of Xi to the 48bit
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[02] spec
ify Xi, param[35] 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.12001.
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 3.05 of the Linux manpages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/manpages/.
20070726 DRAND48(3)
