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: _XOPEN_SOURCE
|| /* Glibc since 2.19: */ _DEFAULT_SOURCE
|| /* Glibc versions <= 2.19: */ _SVID_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 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 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.
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7). 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
POSIX.1-2001, POSIX.1-2008, SVr4.
SEE ALSO
rand(3), random(3)
COLOPHON
This page is part of release 4.09 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
https://www.kernel.org/doc/man-pages/.
2016-03-15 DRAND48(3)
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