RAND(2) RAND(2)
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:
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RAND(2) RAND(2)
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))
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 pro-
duce 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.
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