RAND(2) RAND(2)
NAME
rand, lrand, frand, nrand, lnrand, srand, truerand,
n_truerand, fastrand - random number generator
SYNOPSIS
#include <u.h>
#include <libc.h>
int rand(void)
long lrand(void)
double frand(void)
int nrand(int val)
long lnrand(long val)
void srand(long seed)
ulong truerand(void)
int n_truerand(int val)
ulong fastrand(void)
DESCRIPTION
Rand returns a uniform pseudo-random number x, 0≤x<215.
Lrand returns a uniform long x, 0≤x<231.
Frand returns a uniform double x, 0.0≤x<1.0, This function
calls lrand twice to generate a number with as many as 62
significant bits of mantissa.
Nrand returns a uniform integer x, 0≤x<val. Lnrand is the
same, but returns a long.
The algorithm is additive feedback with:
x[n] = (x[n-273] + x[n-607]) mod 2^31
giving a period of 2^30 × (2^607 - 1).
The generators are initialized by calling srand with what-
ever you like as argument. To get a different starting
value each time,
srand(time(0))
Page 1 Plan 9 (printed 4/25/24)
RAND(2) RAND(2)
will work as long as it is not called more often than once
per second. Calling
srand(1)
will initialize the generators to their starting state.
Truerand returns a random unsigned long read from
/dev/random. Due to the nature of /dev/random, truerand can
only return a few hundred bits a second.
N_truerand returns a uniform integer x, 0≤x<val.
Fastrand is a pseudo random number generator which is seeded
and periodically scrambled using truerand. It is approxi-
mately 1000 times faster than truerand and is intended for
security software that requires a larger stream of unguess-
able data.
SOURCE
/sys/src/libc/port/rand.c
/sys/src/libc/9sys/truerand.c
SEE ALSO
cons(3)
Page 2 Plan 9 (printed 4/25/24)