mirror of
https://github.com/9fans/plan9port.git
synced 2025-01-12 11:10:07 +00:00
193 lines
3.2 KiB
Groff
193 lines
3.2 KiB
Groff
.TH RAND 3
|
||
.SH NAME
|
||
rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, fastrand, nfastrand \- random number generator
|
||
.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 <mp.h>
|
||
.br
|
||
.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 ,
|
||
.RI 0≤ x <2\u\s715\s10\d.
|
||
.PP
|
||
.I Lrand
|
||
returns a uniform
|
||
.B long
|
||
.IR x ,
|
||
.RI 0≤ x <2\u\s731\s10\d.
|
||
.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 .
|
||
Due to the nature of
|
||
.BR /dev/random ,
|
||
truerand can only return a few hundred bits a
|
||
second.
|
||
.PP
|
||
.I Ntruerand
|
||
returns a uniform random integer
|
||
.IR x ,
|
||
.RI 0≤ x < val ≤ 2\u\s732\s10\d-1.
|
||
.PP
|
||
.I 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
|
||
.BR /dev/random .
|
||
.PP
|
||
.I Prng
|
||
uses the native
|
||
.MR rand (3)
|
||
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
|
||
.MR mp (3) ).
|
||
.PP
|
||
.I Fastrand
|
||
uses
|
||
.I genrandom
|
||
to return a uniform
|
||
.B "unsigned long
|
||
.IR x ,
|
||
.RI 0≤ x < 2\u\s732\s10\d-1.
|
||
.PP
|
||
.I Nfastrand
|
||
uses
|
||
.I genrandom
|
||
to return a uniform
|
||
.B "unsigned long
|
||
.IR x ,
|
||
.RI 0≤ x < val ≤ 2\u\s732\s10\d-1.
|
||
.SH SOURCE
|
||
.B \*9/src/lib9
|
||
.br
|
||
.B \*9/src/libsec/port
|
||
.SH "SEE ALSO
|
||
.\" .IR cons (3),
|
||
.MR mp (3)
|
||
.SH BUGS
|
||
.I Truerand
|
||
and
|
||
.I ntruerand
|
||
maintain a static file descriptor.
|
||
.PP
|
||
To avoid name conflicts with the underlying system,
|
||
.IR rand ,
|
||
.IR lrand ,
|
||
.IR frand ,
|
||
.IR nrand ,
|
||
.IR lnrand ,
|
||
and
|
||
.I srand
|
||
are preprocessor macros defined as
|
||
.IR p9rand ,
|
||
.IR p9lrand ,
|
||
and so on;
|
||
see
|
||
.MR intro (3) .
|
||
.ie \n(HT .ds HT "
|
||
.el .ds HT " (see HTML-formatted man page for link)
|
||
.PP
|
||
Some versions of SunOS do not ship with
|
||
.B /dev/random
|
||
installed.
|
||
You may have to download a
|
||
.HR "http://sunsolve.sun.com/search/document.do?assetkey=1-25-27606-1" "patch from Sun\*(HT"
|
||
to add it to your system.
|