term% cat index.txt RAND(2) System Calls Manual RAND(2)
NAME
rand, lrand, frand, nrand, lnrand, srand - 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)
DESCRIPTION
Rand returns a uniform pseudo-random number x, 0â¤x<215.
Lrand returns a uniform long x, 0â¤x<231.
Frand returns a uniform double x, 0.0â¤x<1.0, This function calls lrand
twice to generate a number with as many as 62 significant bits of man‐
tissa.
Nrand returns a uniform integer x, 0â¤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 Ã (2^607 - 1).
The generators are initialized by calling srand with whatever you like
as argument. To get a different starting value each time,
srand(time(0))
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.
Alef
There is no rand in Alef.
SOURCE
/sys/src/libc/port/rand.c
RAND(2)