1.\" Copyright (c) 1983, 1991 The Regents of the University of California. 2.\" All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. 9.\" 2. Redistributions in binary form must reproduce the above copyright 10.\" notice, this list of conditions and the following disclaimer in the 11.\" documentation and/or other materials provided with the distribution. 12.\" 3. All advertising materials mentioning features or use of this software 13.\" must display the following acknowledgement: 14.\" This product includes software developed by the University of 15.\" California, Berkeley and its contributors. 16.\" 4. Neither the name of the University nor the names of its contributors 17.\" may be used to endorse or promote products derived from this software 18.\" without specific prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 21.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 22.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 23.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" 32.\" from: @(#)random.3 6.5 (Berkeley) 4/19/91 33.\" $Id: random.3,v 1.3 1993/10/04 18:05:47 jtc Exp $ 34.\" 35.Dd April 19, 1991 36.Dt RANDOM 3 37.Os BSD 4.2 38.Sh NAME 39.Nm random , 40.Nm srandom , 41.Nm initstate , 42.Nm setstate 43.Nd better random number generator; routines for changing generators 44.Sh SYNOPSIS 45.Fd #include <stdlib.h> 46.Ft long 47.Fn random void 48.Ft void 49.Fn srandom "unsigned seed" 50.Ft char * 51.Fn initstate "unsigned seed" "char *state" "int n" 52.Ft char * 53.Fn setstate "char *state" 54.Sh DESCRIPTION 55The 56.Fn random 57function 58uses a non-linear additive feedback random number generator employing a 59default table of size 31 long integers to return successive pseudo-random 60numbers in the range from 0 to 61.if t 2\u\s731\s10\d\(mi1. 62.if n (2**31)\(mi1. 63The period of this random number generator is very large, approximately 64.if t 16\(mu(2\u\s731\s10\d\(mi1). 65.if n 16*((2**31)\(mi1). 66.Pp 67The 68.Fn random Ns / Fn srandom 69have (almost) the same calling sequence and initialization properties as 70.Xr rand 3 Ns / Xr srand 3 . 71The difference is that 72.Xr rand 73produces a much less random sequence \(em in fact, the low dozen bits 74generated by rand go through a cyclic pattern. All the bits generated by 75.Fn random 76are usable. For example, 77.Sq Li random()&01 78will produce a random binary 79value. 80.Pp 81Unlike 82.Xr srand , 83.Fn srandom 84does not return the old seed; the reason for this is that the amount of 85state information used is much more than a single word. (Two other 86routines are provided to deal with restarting/changing random 87number generators). Like 88.Xr rand 3 , 89however, 90.Fn random 91will by default produce a sequence of numbers that can be duplicated 92by calling 93.Fn srandom 94with 95.Ql 1 96as the seed. 97.Pp 98The 99.Fn initstate 100routine allows a state array, passed in as an argument, to be initialized 101for future use. The size of the state array (in bytes) is used by 102.Fn initstate 103to decide how sophisticated a random number generator it should use \(em the 104more state, the better the random numbers will be. 105(Current "optimal" values for the amount of state information are 1068, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 107the nearest known amount. Using less than 8 bytes will cause an error.) 108The seed for the initialization (which specifies a starting point for 109the random number sequence, and provides for restarting at the same 110point) is also an argument. 111The 112.Fn initstate 113function 114returns a pointer to the previous state information array. 115.Pp 116Once a state has been initialized, the 117.Fn setstate 118routine provides for rapid switching between states. 119The 120.Fn setstate 121function 122returns a pointer to the previous state array; its 123argument state array is used for further random number generation 124until the next call to 125.Fn initstate 126or 127.Fn setstate . 128.Pp 129Once a state array has been initialized, it may be restarted at a 130different point either by calling 131.Fn initstate 132(with the desired seed, the state array, and its size) or by calling 133both 134.Fn setstate 135(with the state array) and 136.Fn srandom 137(with the desired seed). 138The advantage of calling both 139.Fn setstate 140and 141.Fn srandom 142is that the size of the state array does not have to be remembered after 143it is initialized. 144.Pp 145With 256 bytes of state information, the period of the random number 146generator is greater than 147.if t 2\u\s769\s10\d, 148.if n 2**69 149which should be sufficient for most purposes. 150.Sh AUTHOR 151Earl T. Cohen 152.Sh DIAGNOSTICS 153If 154.Fn initstate 155is called with less than 8 bytes of state information, or if 156.Fn setstate 157detects that the state information has been garbled, error 158messages are printed on the standard error output. 159.Sh SEE ALSO 160.Xr rand 3 161.Sh HISTORY 162These 163functions appeared in 164.Bx 4.2 . 165.Sh BUGS 166About 2/3 the speed of 167.Xr rand 3 . 168