RAND(2)RAND(2)NAME
rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, genran‐
dom, 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 man‐
tissa.
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 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 ALSOcons(3), mp(2)BUGS
Truerand and ntruerand maintain a static file descriptor.
RAND(2)