RAND(2)

NAME

rand, lrand, frand, nrand, lnrand, srand − random number generator

SYNOPSIS

#include <u.h>
#include <libc.h>

intrand(void)

longlrand(void)

doublefrand(void)

intnrand(int val)

longlnrand(long val)

voidsrand(long seed)

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 231

giving a period of 230 × (2607 − 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