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DRAND48(3) Linux Programmer's Manual DRAND48(3)
drand48, erand48, lrand48, nrand48, mrand48, jrand48, srand48, seed48, lcong48
- generate uniformly distributed pseudo-random numbers
#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
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.
SVr4, POSIX.1-2001.
These functions are declared obsolete by SVID 3, which states that rand(3)
should be used instead.
rand(3), random(3)
This page is part of release 3.32 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)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface