Berkeley Compatibility Library (libbsd.a)
Reentrant Library (libc_r.a)
SYNOPSIS
#include <stdlib.h>
int rand (void);
int rand_r(
unsigned int *seedptr,
int *randval );
void srand (
unsigned int seed);
PARAMETERS
seed Specifies an initial seed value.
seedptr Points to a seed value, updated at each call.
randval Points to a place to store the random number.
DESCRIPTION
The rand() function returns successive pseudo-random numbers
in the range from 0 (zero) to RAND_MAX. The sequence of
values returned depends on the seed value set with the
srand() function. If rand() is called before any calls to
srand() have been made, the same sequence will be generated
as when srand() is first called with a seed value of 1.
The rand_r() function is the reentrant version of the rand()
function, for use with multi-threaded applications. The
rand_r() function places the seed value at the address
pointed to by seedptr, and places the random number at the
address pointed to by randval.
The srand() function resets the random-number generator to a
random starting point. The generator is initially seeded
with a value of 1.
The rand() function is a very simple random-number genera-
tor. Its spectral properties, the mathematical measurement
of how random the number sequence is, are somewhat weak.
See the drand48() and random() functions for more elaborate
random-number generators that have better spectral proper-
ties.
NOTES
The rand() function is not supported for multi-threaded
applications. Instead, its reentrant equivalent rand_r()
should be used with multiple threads.
The BSD version of the rand() function returns a number in
the range 0 to $ 2 sup 31 $ - 1, rather than 0 to $ 2 sup
15 $ - 1, and can be used by compiling with the Berkeley
Compatibility Library (libbsd.a).
There are better random number generators, as noted above;
however, the rand() and srand() functions are the interfaces
defined for the ANSI C library.
The following functions define the semantics of the rand()
and srand() functions, and are included here to facilitate
porting applications from different implementations:
static unsigned int next = 1;
int rand( )
{
next = next * 1103515245 + 12345;
return ( (next >>16) & RAND_MAX);
}
void srand (seed)
int seed;
{
next = seed
}
AES Support Level:
Full use (rand(), srand())
RETURN VALUES
The rand() function returns the next pseudo-random number in
the sequence.
Upon successful completion, the rand_r() function returns a
value of 0 (zero). Otherwise, -1 is returned and errno is
set to indicate the error.
The srand() function returns no value.
ERRORS
If the rand_r() function fails, errno may be set to the fol-
lowing value:
[EINVAL] Either seedptr or randval is a null pointer.
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RELATED INFORMATION
Functions: drand48(3), random(3)
Acknowledgement and Disclaimer