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 Ns / Fn srandom 68have (almost) the same calling sequence and initialization properties as 69.Xr rand 3 Ns / Xr srand 3 . 70The difference is that 71.Xr rand 72produces a much less random sequence \(em in fact, the low dozen bits 73generated by rand go through a cyclic pattern. All the bits generated by 74.Fn random 75are usable. For example, 76.Sq Li random()&01 77will produce a random binary 78value. 79.Pp 80Unlike 81.Xr srand , 82.Fn srandom 83does not return the old seed; the reason for this is that the amount of 84state information used is much more than a single word. (Two other 85routines are provided to deal with restarting/changing random 86number generators). Like 87.Xr rand 3 , 88however, 89.Fn random 90will by default produce a sequence of numbers that can be duplicated 91by calling 92.Fn srandom 93with 94.Ql 1 95as the seed. 96.Pp 97The 98.Fn initstate 99routine allows a state array, passed in as an argument, to be initialized 100for future use. The size of the state array (in bytes) is used by 101.Fn initstate 102to decide how sophisticated a random number generator it should use \(em the 103more state, the better the random numbers will be. 104(Current "optimal" values for the amount of state information are 1058, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 106the nearest known amount. Using less than 8 bytes will cause an error.) 107The seed for the initialization (which specifies a starting point for 108the random number sequence, and provides for restarting at the same 109point) is also an argument. 110The 111.Fn initstate 112function 113returns a pointer to the previous state information array. 114.Pp 115Once a state has been initialized, the 116.Fn setstate 117routine provides for rapid switching between states. 118The 119.Fn setstate 120function 121returns a pointer to the previous state array; its 122argument state array is used for further random number generation 123until the next call to 124.Fn initstate 125or 126.Fn setstate . 127.Pp 128Once a state array has been initialized, it may be restarted at a 129different point either by calling 130.Fn initstate 131(with the desired seed, the state array, and its size) or by calling 132both 133.Fn setstate 134(with the state array) and 135.Fn srandom 136(with the desired seed). 137The advantage of calling both 138.Fn setstate 139and 140.Fn srandom 141is that the size of the state array does not have to be remembered after 142it is initialized. 143.Pp 144With 256 bytes of state information, the period of the random number 145generator is greater than 146.if t 2\u\s769\s10\d, 147.if n 2**69 148which should be sufficient for most purposes. 149.Sh AUTHOR 150Earl T. Cohen 151.Sh DIAGNOSTICS 152If 153.Fn initstate 154is called with less than 8 bytes of state information, or if 155.Fn setstate 156detects that the state information has been garbled, error 157messages are printed on the standard error output. 158.Sh SEE ALSO 159.Xr rand 3 160.Sh HISTORY 161These 162functions appeared in 163.Bx 4.2 . 164.Sh BUGS 165About 2/3 the speed of 166.Xr rand 3 . 167