NAME
rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, genrandom, prng, fastrand, nfastrand – random number generators

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)

ulong    ntruerand(ulong val)
#include <mp.h>
#include <libsec.h>

void     genrandom(uchar *buf, int nbytes)

void     prng(uchar *buf, int nbytes)

ulong    fastrand(void)

ulong    nfastrand(ulong val)

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.

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.

Ntruerand returns a uniform random integer x, 0≤x<val≤232–1.

Genrandom fills a buffer with bytes from the X9.17 pseudo–random number generator. The X9.17 generator is seeded by 24 truly random bytes read from /dev/random.

Prng uses the native rand(2) pseudo–random number generator to fill the buffer. Used with srand, this function can produce a reproducible stream of pseudo random numbers useful in testing.

Both genrandom and prng may be passed to mprand (see mp(2)).

Fastrand uses genrandom to return a uniform unsigned long x, 0≤x<232–1.

Nfastrand uses genrandom to return a uniform unsigned long x, 0≤x<val≤232–1.

SOURCE
/sys/src/libc/port/*rand.c
/sys/src/libc/9sys/truerand.c
/sys/src/libsec/port/genrandom.c
/sys/src/libsec/port/prng.c
/sys/src/libsec/port/*fastrand.c

SEE ALSO
cons(3), mp(2)

BUGS
Truerand and ntruerand maintain a static file descriptor.
Copyright © 2017 Alcatel-Lucent. All rights reserved.