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 int xsubi[3]);
long int lrand48(void);
long int nrand48(unsigned short int xsubi[3]);
long int mrand48(void);
long int jrand48(unsigned short int xsubi[3]);
void srand48(long int seedval));
unsigned short int *seed48(unsignedshortint seed16v [3]);
void lcong48(unsigned short int param[7]);
DESCRIPTION
These functions generate pseudo-random numbers using the
linear congruential algorithm and 48-bit integer arithmetic.
The drand48() and erand48() functions return non-negative
double-precision floating-point values uniformly distributed
between [0.0, 1.0).
The lrand48() and nrand48() functions return non-negative
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 initial-
ization functions, one of which should be called before
using drand48(), lrand48() or mrand49(). The functions
erand48(), nrand48() and jrand48() do not require an ini-
tialization 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
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 func-
tions 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 cal-
ling 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 ele-
ments 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
SVID 3
NOTES
These functions are declared obsolete by SVID 3, which
states that rand(3) should be used instead.
SEE ALSO
rand(3), random(3)