From 78e51a8c6678b6e3dff3d619aa786669f531f4bc Mon Sep 17 00:00:00 2001 From: rsc Date: Fri, 14 Jan 2005 03:45:44 +0000 Subject: checkpoint --- man/man3/rand.html | 190 +++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 190 insertions(+) create mode 100644 man/man3/rand.html (limited to 'man/man3/rand.html') diff --git a/man/man3/rand.html b/man/man3/rand.html new file mode 100644 index 00000000..0601c6bf --- /dev/null +++ b/man/man3/rand.html @@ -0,0 +1,190 @@ + +rand(3) - Plan 9 from User Space + + + + +
+
+
RAND(3)RAND(3) +
+
+

NAME
+ +
+ + rand, lrand, frand, nrand, lnrand, srand, truerand, ntruerand, + fastrand, nfastrand – random number generator
+ +
+

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:
+ +
+ + x[n] = (x[n-273] + x[n-607]) mod 231 +
+ + +
+ giving a period of 230 × (2607 – 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(3) 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(3)). +
+ + 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
+ +
+ + /usr/local/plan9/src/lib9
+ /usr/local/plan9/src/libsec/port
+ +
+

SEE ALSO
+ +
+ + mp(3)
+ +
+

BUGS
+ +
+ + Truerand and ntruerand maintain a static file descriptor. +
+ + To avoid name conflicts with the underlying system, rand, lrand, + frand, nrand, lnrand, and srand are preprocessor macros defined + as p9rand, p9lrand, and so on; see intro(3).
+ +
+ +

 +
+
+ + +
+
+
+Space Glenda +
+
+ + -- cgit v1.2.3