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 1.13 2001/06/09 01:41:59 assar Exp $ 33.\" 34.Dd April 19, 1991 35.Dt RANDOM 3 36.Os 37.Sh NAME 38.Nm random , 39.Nm srandom , 40.Nm srandomdev , 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 int seed" 50.Ft void 51.Fn srandomdev void 52.Ft char * 53.Fn initstate "unsigned int seed" "char *state" "size_t n" 54.Ft char * 55.Fn setstate "const char *state" 56.Sh DESCRIPTION 57The 58.Fn random 59function uses a non-linear additive feedback random number generator employing 60a default table of size 31 long integers to return successive pseudo-random 61numbers in the range from 0 to (2**31)\-1. 62The period of this random number generator is very large, approximately 6316*((2**31)\-1. 64.Pp 65The 66.Fn random 67and 68.Fn srandom 69functions have (almost) the same calling sequence and initialization 70properties as 71.Xr rand 3 Ns / Xr srand 3 . 72The difference is that 73.Xr rand 74produces a much less random sequence \(em in fact, the low dozen bits 75generated by rand go through a cyclic pattern. 76All the bits generated by 77.Fn random 78are usable. 79For example, 80.Sq Li random()&01 81will produce a random binary 82value. 83.Pp 84Like 85.Xr rand 3 , 86.Fn random 87will by default produce a sequence of numbers that can be duplicated 88by calling 89.Fn srandom 90with 91.Ql 1 92as the seed. 93.Pp 94The 95.Fn srandomdev 96routine initialize a state array using the 97.Xr arandom 4 98random number device which returns good random numbers, 99suitable for cryptographic use. 100Note that this particular seeding procedure can generate 101states which are impossible to reproduce by calling 102.Fn srandom 103with any value, since the succeeding terms in the 104state buffer are no longer derived from the LC algorithm applied to 105a fixed seed. 106.Pp 107The 108.Fn initstate 109routine allows a state array, passed in as an argument, to be initialized 110for future use. 111The size of the state array (in bytes) is used by 112.Fn initstate 113to decide how sophisticated a random number generator it should use \(em the 114more state, the better the random numbers will be. 115(Current "optimal" values for the amount of state information are 1168, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 117the nearest known amount. 118Using less than 8 bytes will cause an error.) 119The seed for the initialization (which specifies a starting point for 120the random number sequence, and provides for restarting at the same 121point) is also an argument. 122The 123.Fn initstate 124function returns a pointer to the previous state information array. 125.Pp 126Once a state has been initialized, the 127.Fn setstate 128routine provides for rapid switching between states. 129The 130.Fn setstate 131function returns a pointer to the previous state array; its 132argument state array is used for further random number generation 133until the next call to 134.Fn initstate 135or 136.Fn setstate . 137.Pp 138Once a state array has been initialized, it may be restarted at a 139different point either by calling 140.Fn initstate 141(with the desired seed, the state array, and its size) or by calling 142both 143.Fn setstate 144(with the state array) and 145.Fn srandom 146(with the desired seed). 147The advantage of calling both 148.Fn setstate 149and 150.Fn srandom 151is that the size of the state array does not have to be remembered after 152it is initialized. 153.Pp 154With 256 bytes of state information, the period of the random number 155generator is greater than 2**69 156which should be sufficient for most purposes. 157.Sh AUTHORS 158.An Earl T. Cohen 159.Sh DIAGNOSTICS 160If 161.Fn initstate 162is called with less than 8 bytes of state information, or if 163.Fn setstate 164detects that the state information has been garbled, error 165messages are printed on the standard error output. 166.Sh SEE ALSO 167.Xr arc4random 3 , 168.Xr drand48 3 , 169.Xr rand 3 , 170.Xr random 4 , 171.Sh STANDARDS 172The 173.Fn random , 174.Fn srandom , 175.Fn initstate , 176and 177.Fn setstate 178functions conform to 179.St -xpg4.2 . 180.Pp 181The 182.Fn srandomdev 183function is an extension. 184.Sh HISTORY 185These 186functions appeared in 187.Bx 4.2 . 188.Sh BUGS 189About 2/3 the speed of 190.Xr rand 3 . 191