1.\" Copyright (c) 1983, 1991, 1993 2.\" The Regents of the University of California. 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.\" @(#)random.3 8.1 (Berkeley) 6/4/93 33.\" 34.Dd June 4, 1993 35.Dt RANDOM 3 36.Os BSD 4.2 37.Sh NAME 38.Nm random , 39.Nm srandom , 40.Nm initstate , 41.Nm setstate 42.Nd better random number generator; routines for changing generators 43.Sh SYNOPSIS 44.Fd #include <stdlib.h> 45.Ft long 46.Fn random void 47.Ft void 48.Fn srandom "unsigned seed" 49.Ft char * 50.Fn initstate "unsigned seed" "char *state" "int n" 51.Ft char * 52.Fn setstate "char *state" 53.Sh DESCRIPTION 54The 55.Fn random 56function 57uses a non-linear additive feedback random number generator employing a 58default table of size 31 long integers to return successive pseudo-random 59numbers in the range from 0 to 60.if t 2\u\s731\s10\d\(mi1. 61.if n (2**31)\(mi1. 62The period of this random number generator is very large, approximately 63.if t 16\(mu(2\u\s731\s10\d\(mi1). 64.if n 16*((2**31)\(mi1). 65.Pp 66The 67.Fn random 68and 69.Fn srandom 70functions have (almost) the same calling sequence and initialization properties as the 71.Xr rand 3 72and 73.Xr srand 3 74functions. 75The difference is that 76.Xr rand 3 77produces a much less random sequence \(em in fact, the low dozen bits 78generated by rand go through a cyclic pattern. All the bits generated by 79.Fn random 80are usable. For example, 81.Sq Li random()&01 82will produce a random binary 83value. 84.Pp 85Unlike 86.Xr srand , 87.Fn srandom 88does not return the old seed; the reason for this is that the amount of 89state information used is much more than a single word. (Two other 90routines are provided to deal with restarting/changing random 91number generators). Like 92.Xr rand 3 , 93however, 94.Fn random 95will by default produce a sequence of numbers that can be duplicated 96by calling 97.Fn srandom 98with 99.Ql 1 100as the seed. 101.Pp 102The 103.Fn initstate 104routine allows a state array, passed in as an argument, to be initialized 105for future use. The size of the state array (in bytes) is used by 106.Fn initstate 107to decide how sophisticated a random number generator it should use \(em the 108more state, the better the random numbers will be. 109(Current "optimal" values for the amount of state information are 1108, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 111the nearest known amount. Using less than 8 bytes will cause an error.) 112The seed for the initialization (which specifies a starting point for 113the random number sequence, and provides for restarting at the same 114point) is also an argument. 115The 116.Fn initstate 117function 118returns a pointer to the previous state information array. 119.Pp 120Once a state has been initialized, the 121.Fn setstate 122routine provides for rapid switching between states. 123The 124.Fn setstate 125function 126returns a pointer to the previous state array; its 127argument state array is used for further random number generation 128until the next call to 129.Fn initstate 130or 131.Fn setstate . 132.Pp 133Once a state array has been initialized, it may be restarted at a 134different point either by calling 135.Fn initstate 136(with the desired seed, the state array, and its size) or by calling 137both 138.Fn setstate 139(with the state array) and 140.Fn srandom 141(with the desired seed). 142The advantage of calling both 143.Fn setstate 144and 145.Fn srandom 146is that the size of the state array does not have to be remembered after 147it is initialized. 148.Pp 149With 256 bytes of state information, the period of the random number 150generator is greater than 151.if t 2\u\s769\s10\d, 152.if n 2**69 153which should be sufficient for most purposes. 154.Sh AUTHOR 155Earl T. Cohen 156.Sh DIAGNOSTICS 157If 158.Fn initstate 159is called with less than 8 bytes of state information, or if 160.Fn setstate 161detects that the state information has been garbled, error 162messages are printed on the standard error output. 163.Sh SEE ALSO 164.Xr rand 3 165.Sh HISTORY 166These 167functions appeared in 168.Bx 4.2 . 169.Sh BUGS 170About 2/3 the speed of 171.Xr rand 3 . 172