TH RAND 2
SH NAME
rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, genrandom, prng, fastrand, nfastrand \- random number generators
SH SYNOPSIS
B #include <u.h>
br
B #include <libc.h>
PP
ta \w'\fLdouble 'u
B
int rand(void)
PP
B
long lrand(void)
PP
B
double frand(void)
PP
B
int nrand(int val)
PP
B
long lnrand(long val)
PP
B
void srand(long seed)
PP
B
ulong truerand(void)
PP
B
ulong ntruerand(ulong val)
sp
B #include <libsec.h>
PP
B
void genrandom(uchar *buf, int nbytes)
PP
B
void prng(uchar *buf, int nbytes)
PP
B
ulong fastrand(void)
PP
B
ulong nfastrand(ulong val)
SH DESCRIPTION
I Rand
returns a uniform pseudo-random
number
IR x ,
if t 0≤ \fIx\fR <2\u\s715\s10\d.
if n 0≤ x <2^15.
PP
I Lrand
returns a uniform
B long
IR x ,
if t 0≤ \fIx\fR <2\u\s731\s10\d.
if n 0≤ x <2^31.
PP
I Frand
returns a uniform
B double
IR x ,
RI 0.0≤ x <1.0,
This function calls
I lrand
twice to generate a number with as many as 62 significant bits of mantissa.
PP
I Nrand
returns a uniform integer
IR x ,
RI 0≤ x < val.
I Lnrand
is the same, but returns a
BR long .
PP
The algorithm is additive feedback with:
IP
x[n] = (x[n\(mi273] + x[n\(mi607]) mod
if t 2\u\s731\s0\d
if n 2^31
LP
giving a period of
if t 2\u\s730\s10\d \(mu (2\u\s7607\s10\d \- 1).
if n 2^30 × (2^607 - 1).
PP
The generators are initialized by calling
I srand
with whatever you like as argument.
To get a different starting value each time,
IP
L
srand(time(0))
LP
will work as long as it is not called more often
than once per second.
Calling
IP
L
srand(1)
LP
will initialize the generators to their
starting state.
PP
I Truerand
returns a random unsigned long read from
BR /dev/random .
PP
I Ntruerand
returns a uniform random integer
IR x ,
if t 0≤ \fIx\fR < \fIval\fR ≤ 2\u\s732\s10\d-1.
if n 0≤ x < val ≤ 2^32-1.
PP
I Genrandom
fills a buffer with bytes from the cryptographic pseudo-random
number generator. The generator is automatically seeded by
IR truerand .
PP
I Prng
uses the native
IR rand (2)
pseudo-random number generator to fill the buffer. Used with
IR srand ,
this function can produce a reproducible stream of pseudo random
numbers useful in testing.
PP
Both
I genrandom
and
I prng
may be passed to
I mprand
(see
IR mp (2)).
PP
I Fastrand
uses
I genrandom
to return a uniform
B "unsigned long
IR x ,
if t 0≤ \fIx\fR <2\u\s732\s10\d-1.
if n 0≤ x <2^32-1.
PP
I Nfastrand
uses
I genrandom
to return a uniform
B "unsigned long
IR x ,
if t 0≤ \fIx\fR < \fIval\fR ≤ 2\u\s732\s10\d-1.
if n 0≤ x < val ≤ 2^32-1.
SH SOURCE
B /sys/src/libc/port/*rand.c
br
B /sys/src/libc/9sys/truerand.c
br
B /sys/src/libsec/port/genrandom.c
br
B /sys/src/libsec/port/prng.c
br
B /sys/src/libsec/port/*fastrand.c
SH "SEE ALSO
IR cons (3),
IR mp (2)
SH BUGS
I Truerand
and
I ntruerand
maintain a static file descriptor.
