diff options
Diffstat (limited to 'lib/libc/stdlib/random.3')
| -rw-r--r-- | lib/libc/stdlib/random.3 | 167 |
1 files changed, 167 insertions, 0 deletions
diff --git a/lib/libc/stdlib/random.3 b/lib/libc/stdlib/random.3 new file mode 100644 index 00000000000..1de9fba4bef --- /dev/null +++ b/lib/libc/stdlib/random.3 @@ -0,0 +1,167 @@ +.\" Copyright (c) 1983, 1991 The Regents of the University of California. +.\" All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. All advertising materials mentioning features or use of this software +.\" must display the following acknowledgement: +.\" This product includes software developed by the University of +.\" California, Berkeley and its contributors. +.\" 4. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.\" from: @(#)random.3 6.5 (Berkeley) 4/19/91 +.\" $Id: random.3,v 1.1 1995/10/18 08:42:19 deraadt Exp $ +.\" +.Dd April 19, 1991 +.Dt RANDOM 3 +.Os BSD 4.2 +.Sh NAME +.Nm random , +.Nm srandom , +.Nm initstate , +.Nm setstate +.Nd better random number generator; routines for changing generators +.Sh SYNOPSIS +.Fd #include <stdlib.h> +.Ft long +.Fn random void +.Ft void +.Fn srandom "unsigned seed" +.Ft char * +.Fn initstate "unsigned seed" "char *state" "int n" +.Ft char * +.Fn setstate "char *state" +.Sh DESCRIPTION +The +.Fn random +function +uses a non-linear additive feedback random number generator employing a +default table of size 31 long integers to return successive pseudo-random +numbers in the range from 0 to +.if t 2\u\s731\s10\d\(mi1. +.if n (2**31)\(mi1. +The period of this random number generator is very large, approximately +.if t 16\(mu(2\u\s731\s10\d\(mi1). +.if n 16*((2**31)\(mi1). +.Pp +The +.Fn random Ns / Fn srandom +have (almost) the same calling sequence and initialization properties as +.Xr rand 3 Ns / Xr srand 3 . +The difference is that +.Xr rand +produces a much less random sequence \(em in fact, the low dozen bits +generated by rand go through a cyclic pattern. All the bits generated by +.Fn random +are usable. For example, +.Sq Li random()&01 +will produce a random binary +value. +.Pp +Unlike +.Xr srand , +.Fn srandom +does not return the old seed; the reason for this is that the amount of +state information used is much more than a single word. (Two other +routines are provided to deal with restarting/changing random +number generators). Like +.Xr rand 3 , +however, +.Fn random +will by default produce a sequence of numbers that can be duplicated +by calling +.Fn srandom +with +.Ql 1 +as the seed. +.Pp +The +.Fn initstate +routine allows a state array, passed in as an argument, to be initialized +for future use. The size of the state array (in bytes) is used by +.Fn initstate +to decide how sophisticated a random number generator it should use \(em the +more state, the better the random numbers will be. +(Current "optimal" values for the amount of state information are +8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to +the nearest known amount. Using less than 8 bytes will cause an error.) +The seed for the initialization (which specifies a starting point for +the random number sequence, and provides for restarting at the same +point) is also an argument. +The +.Fn initstate +function +returns a pointer to the previous state information array. +.Pp +Once a state has been initialized, the +.Fn setstate +routine provides for rapid switching between states. +The +.Fn setstate +function +returns a pointer to the previous state array; its +argument state array is used for further random number generation +until the next call to +.Fn initstate +or +.Fn setstate . +.Pp +Once a state array has been initialized, it may be restarted at a +different point either by calling +.Fn initstate +(with the desired seed, the state array, and its size) or by calling +both +.Fn setstate +(with the state array) and +.Fn srandom +(with the desired seed). +The advantage of calling both +.Fn setstate +and +.Fn srandom +is that the size of the state array does not have to be remembered after +it is initialized. +.Pp +With 256 bytes of state information, the period of the random number +generator is greater than +.if t 2\u\s769\s10\d, +.if n 2**69 +which should be sufficient for most purposes. +.Sh AUTHOR +Earl T. Cohen +.Sh DIAGNOSTICS +If +.Fn initstate +is called with less than 8 bytes of state information, or if +.Fn setstate +detects that the state information has been garbled, error +messages are printed on the standard error output. +.Sh SEE ALSO +.Xr rand 3 +.Sh HISTORY +These +functions appeared in +.Bx 4.2 . +.Sh BUGS +About 2/3 the speed of +.Xr rand 3 . |