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drand48(3c)
drand48(3C) Standard C Library Functions drand48(3C)
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 lrand48(void)
long nrand48(unsigned short xsubi[3]);
long mrand48(void)
long jrand48(unsigned short xsubi[3]);
void srand48(long seedval);
unsigned short *seed48(unsigned short seed16v[3]);
void lcong48(unsigned short param[7]);
int drand48_r(struct drand48_data *buffer, double *result);
int erand48_r(unsigned short xsubi[3],
struct drand48_data *buf, double *result);
int lrand48_r(struct drand48_data *buf, long int *result);
int nrand48_r(unsigned short int xsubi[3],
struct drand48_data *buf, long int *result);
int mrand48_r(struct drand48_data *buf, long int *result);
int jrand48_r(unsigned short int xsubi[3],
struct drand48_data *buf, long int *result);
int srand48_r(long int seedval, struct drand48_data *buf);
int seed48_r(unsigned short int seed16v[3],
struct drand48_data *buf);
int lcong48_r(unsigned short int param[7],
struct drand48_data *buf);
DESCRIPTION
This family of functions generates pseudo-random numbers using the
well-known linear congruential algorithm and 48-bit integer arithmetic.
Functions drand48() and erand48() return non-negative double-precision
floating-point values uniformly distributed over the interval [0.0,
1.0).
Functions lrand48() and nrand48() return non-negative long integers
uniformly distributed over the interval [0, 2 ^31 ].
Functions mrand48() and jrand48() return signed long integers uniformly
distributed over the interval [-2 ^31 , 2 ^31 ].
Functions srand48(), seed48(), and lcong48() are initialization entry
points, one of which should be invoked before either drand48(),
lrand48(), or mrand48() is called. (Although it is not recommended
practice, constant default initializer values will be supplied automat‐
ically if drand48(), lrand48(), or mrand48() is called without a prior
call to an initialization entry point.) Functions erand48(), nrand48(),
and jrand48() do not require an initialization entry point to be called
first.
All the routines work by generating a sequence of 48-bit integer val‐
ues, X(i), according to the linear congruential formula
X(n+1)= (aX (n)+c)(mod m) n>=0.
The parameter m = 2^48; hence 48-bit integer arithmetic is performed.
Unless lcong48() has been invoked, the multiplier value a and the ad‐
dend value c are given by
a = 5DEECE66D(16) = 273673163155(8)
c = B(16) = 13(8)
The value returned by any of the functions drand48(), erand48(),
lrand48(), nrand48(), mrand48(), or jrand48() is computed by first gen‐
erating the next 48-bit X(i) in the sequence. Then the appropriate num‐
ber of bits, according to the type of data item to be returned, are
copied from the high-order (leftmost) bits of X(i) and transformed into
the returned value.
The functions drand48(), lrand48(), and mrand48() store the last 48-bit
X(i) generated in an internal buffer. X(i) must be initialized prior to
being invoked. The functions erand48(), nrand48(), and jrand48() re‐
quire the calling program to provide storage for the successive X(i)
values in the array specified as an argument when the functions are in‐
voked. These routines do not have to be initialized; the calling pro‐
gram must place the desired initial value of X(i) into the array and
pass it as an argument. By using different arguments, functions
erand48(), nrand48(), and jrand48() allow separate modules of a large
program to generate several independent streams of pseudo-random num‐
bers, that is, the sequence of numbers in each stream will not depend
upon how many times the routines have been called to generate numbers
for the other streams.
The initializer function srand48() sets the high-order 32 bits of X(i)
to the 32 bits contained in its argument. The low-order 16 bits of X(i)
are set to the arbitrary value 330E(16) .
The initializer function seed48() sets the value of X(i) to the 48-bit
value specified in the argument array. In addition, the previous value
of X(i) is copied into a 48-bit internal buffer, used only by seed48(),
and a pointer to this buffer is the value returned by seed48(). This
returned pointer, which can just be ignored if not needed, is useful if
a program is to be restarted from a given point at some future time —
use the pointer to get at and store the last X(i) value, and then use
this value to reinitialize using seed48() when the program is
restarted.
The initialization function lcong48() allows the user to specify the
initial X(i) the multiplier value a, and the addend value c. Argument
array elements param[0-2] specify X(i), param[3-5] specify the multi‐
plier a, and param[6] specifies the 16-bit addend c. After lcong48()
has been called, a subsequent call to either srand48() or seed48() will
restore the "standard" multiplier and addend values, a and c, specified
above.
Functions drand48_r(), erand48_r(), jrand48_r(), lrand48_r(),
mrand_r(), and nrand_r() are reentrant versions of drand48(),
erand48(), jrand48(), lrand48(), mrand48(), and nrand48() functions.
They use the supplied buffer, buf, to store the random number generator
state, as opposed to the global buffers used by the non-reentrant func‐
tions. The buffer must be first allocated, and then initialized either
by filling with zeroes, or by calling one of the srand48_r(),
seed48_r(), or lcong48_r() functions.
Functions srand48_r(), seed48_r(), and lcong48_r() are reentrant ver‐
sions of the functions srand48(), seed48(), and lcong48(). In addition,
they can be used to initialize the supplied buffer, buf.
USAGE
Programmers should use /dev/urandom or /dev/random for most random-num‐
ber generation, especially for cryptographic purposes. See getrandom(2)
and random(4D).
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Interface StabilityCommitted _ MT-LevelSafe _ Standard‐
See standards(7).
SEE ALSO
getrandom(2), rand(3C), random(4D), attributes(7), standards(7)
Oracle Solaris 11.4 10 Mar 2022 drand48(3C)