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.\" $OpenBSD: random.3,v 1.6 1998/07/05 19:54:25 millert Exp $ 33.\" 34.Dd April 19, 1991 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 int seed" 49.Ft char * 50.Fn initstate "unsigned int seed" "char *state" "size_t n" 51.Ft char * 52.Fn setstate "const 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 maximum value returned by 63.Fn random 64is 65.Dv LONG_MAX 66(as defined by the header file 67.Aq Pa limits.h ) . 68The period of this random number generator is very large, approximately 69.if t 16\(mu(2\u\s731\s10\d\(mi1). 70.if n 16*((2**31)\(mi1). 71.Pp 72The 73.Fn random Ns / Fn srandom 74have (almost) the same calling sequence and initialization properties as 75.Xr rand 3 Ns / Xr srand 3 . 76The difference is that 77.Xr rand 78produces a much less random sequence \(em in fact, the low dozen bits 79generated by rand go through a cyclic pattern. All the bits generated by 80.Fn random 81are usable. For example, 82.Sq Li random()&01 83will produce a random binary 84value. 85.Pp 86Unlike 87.Xr srand , 88.Fn srandom 89does not return the old seed; the reason for this is that the amount of 90state information used is much more than a single word. (Two other 91routines are provided to deal with restarting/changing random 92number generators). Like 93.Xr rand 3 , 94however, 95.Fn random 96will by default produce a sequence of numbers that can be duplicated 97by calling 98.Fn srandom 99with 100.Ql 1 101as the seed. 102.Pp 103The 104.Fn initstate 105routine allows a state array, passed in as an argument, to be initialized 106for future use. The size of the state array (in bytes) is used by 107.Fn initstate 108to decide how sophisticated a random number generator it should use \(em the 109more state, the better the random numbers will be. 110(Current "optimal" values for the amount of state information are 1118, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 112the nearest known amount. Using less than 8 bytes will cause an error.) 113The seed for the initialization (which specifies a starting point for 114the random number sequence, and provides for restarting at the same 115point) is also an argument. 116The 117.Fn initstate 118function 119returns a pointer to the previous state information array. 120.Pp 121Once a state has been initialized, the 122.Fn setstate 123routine provides for rapid switching between states. 124The 125.Fn setstate 126function 127returns a pointer to the previous state array; its 128argument state array is used for further random number generation 129until the next call to 130.Fn initstate 131or 132.Fn setstate . 133.Pp 134Once a state array has been initialized, it may be restarted at a 135different point either by calling 136.Fn initstate 137(with the desired seed, the state array, and its size) or by calling 138both 139.Fn setstate 140(with the state array) and 141.Fn srandom 142(with the desired seed). 143The advantage of calling both 144.Fn setstate 145and 146.Fn srandom 147is that the size of the state array does not have to be remembered after 148it is initialized. 149.Pp 150With 256 bytes of state information, the period of the random number 151generator is greater than 152.if t 2\u\s769\s10\d, 153.if n 2**69 154which should be sufficient for most purposes. 155.Sh AUTHOR 156Earl T. Cohen 157.Sh DIAGNOSTICS 158If 159.Fn initstate 160is called with less than 8 bytes of state information, or if 161.Fn setstate 162detects that the state information has been garbled, error 163messages are printed on the standard error output. 164.Sh SEE ALSO 165.Xr arc4random 3 , 166.Xr drand48 3 , 167.Xr rand 3 168.Sh STANDARDS 169The 170.Fn random , 171.Fn srandom , 172.Fn initstate , 173and 174.Fn setstate 175functions conform to 176.St -xpg4.2 . 177.Sh HISTORY 178These 179functions appeared in 180.Bx 4.2 . 181.Sh BUGS 182About 2/3 the speed of 183.Xr rand 3 . 184