10564b1175
groff 1.23.0 added .MR to its -man macro package. The NEWS file states
that the inclusion of the macro "was prompted by its introduction to
Plan 9 from User Space's troff in August 2020." From d32deab it seems
that the name for Plan 9 from User Space's implementation was suggested
by groff maintainer G. Brandon Robinson.
Not sure if the intention was to make these definitions compatible, but
it would be nice if they were.
Currently, Plan 9 from User Space's .MR expects its second argument to
be parenthesized. groff's .MR does not. This results in extra
parentheses appearing in manual references when viewing Plan 9 from User
Space's manual pages on a system using groff.
194 lines
3.2 KiB
Groff
194 lines
3.2 KiB
Groff
.TH RAND 3
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.SH NAME
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rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, fastrand, nfastrand \- random number generator
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.SH SYNOPSIS
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.B #include <u.h>
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.br
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.B #include <libc.h>
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.PP
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.ta \w'\fLdouble 'u
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.B
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int rand(void)
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.PP
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.B
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long lrand(void)
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.PP
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.B
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double frand(void)
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.PP
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.B
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int nrand(int val)
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.PP
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.B
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long lnrand(long val)
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.PP
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.B
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void srand(long seed)
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.PP
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.B
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ulong truerand(void)
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.PP
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.B
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ulong ntruerand(ulong val)
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.sp
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.B #include <mp.h>
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.br
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.B #include <libsec.h>
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.PP
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.B
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void genrandom(uchar *buf, int nbytes)
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.PP
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.B
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void prng(uchar *buf, int nbytes)
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.PP
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.B
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ulong fastrand(void)
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.PP
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.B
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ulong nfastrand(ulong val)
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.SH DESCRIPTION
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.I Rand
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returns a uniform pseudo-random
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number
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.IR x ,
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.RI 0≤ x <2\u\s715\s10\d.
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.PP
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.I Lrand
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returns a uniform
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.B long
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.IR x ,
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.RI 0≤ x <2\u\s731\s10\d.
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.PP
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.I Frand
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returns a uniform
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.B double
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.IR x ,
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.RI 0.0≤ x <1.0,
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This function calls
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.I lrand
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twice to generate a number with as many as 62 significant bits of mantissa.
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.PP
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.I Nrand
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returns a uniform integer
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.IR x ,
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.RI 0≤ x < val.
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.I Lnrand
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is the same, but returns a
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.BR long .
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.PP
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The algorithm is additive feedback with:
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.IP
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x[n] = (x[n\(mi273] + x[n\(mi607]) mod
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.if t 2\u\s731\s0\d
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.if n 2^31
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.LP
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giving a period of
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.if t 2\u\s730\s10\d \(mu (2\u\s7607\s10\d \- 1).
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.if n 2^30 × (2^607 - 1).
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.PP
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The generators are initialized by calling
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.I srand
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with whatever you like as argument.
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To get a different starting value each time,
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.IP
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.L
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srand(time(0))
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.LP
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will work as long as it is not called more often
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than once per second.
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Calling
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.IP
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.L
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srand(1)
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.LP
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will initialize the generators to their
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starting state.
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.PP
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.I Truerand
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returns a random unsigned long read from
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.BR /dev/random .
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Due to the nature of
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.BR /dev/random ,
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truerand can only return a few hundred bits a
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second.
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.PP
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.I Ntruerand
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returns a uniform random integer
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.IR x ,
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.RI 0≤ x < val ≤ 2\u\s732\s10\d-1.
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.PP
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.I Genrandom
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fills a buffer with bytes from the X9.17 pseudo-random
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number generator. The X9.17 generator is seeded by 24
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truly random bytes read from
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.BR /dev/random .
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.PP
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.I Prng
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uses the native
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.MR rand 3
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pseudo-random number generator to fill the buffer. Used with
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.IR srand ,
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this function can produce a reproducible stream of pseudo random
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numbers useful in testing.
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.PP
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Both
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.I genrandom
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and
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.I prng
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may be passed to
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.I mprand
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(see
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.MR mp 3 ).
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.PP
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.I Fastrand
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uses
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.I genrandom
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to return a uniform
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.B "unsigned long
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.IR x ,
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.RI 0≤ x < 2\u\s732\s10\d-1.
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.PP
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.I Nfastrand
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uses
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.I genrandom
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to return a uniform
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.B "unsigned long
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.IR x ,
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.RI 0≤ x < val ≤ 2\u\s732\s10\d-1.
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.SH SOURCE
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.B \*9/src/lib9
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.br
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.B \*9/src/libsec/port
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.SH "SEE ALSO
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.\" .IR cons (3),
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.MR mp 3
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.SH BUGS
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.I Truerand
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and
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.I ntruerand
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maintain a static file descriptor.
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.PP
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To avoid name conflicts with the underlying system,
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.IR rand ,
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.IR lrand ,
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.IR frand ,
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.IR nrand ,
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.IR lnrand ,
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and
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.I srand
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are preprocessor macros defined as
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.IR p9rand ,
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.IR p9lrand ,
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and so on;
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see
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.MR intro 3 .
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.ie \n(HT .ds HT "
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.el .ds HT " (see HTML-formatted man page for link)
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.PP
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Some versions of SunOS do not ship with
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.B /dev/random
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installed.
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You may have to download a
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.HR "http://sunsolve.sun.com/search/document.do?assetkey=1-25-27606-1" "patch from Sun\*(HT"
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to add it to your system.
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