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 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 long seed" 50.Ft void 51.Fn srandomdev void 52.Ft char * 53.Fn initstate "unsigned long seed" "char *state" "long n" 54.Ft char * 55.Fn setstate "char *state" 56.Sh DESCRIPTION 57The 58.Fn random 59function 60uses a non-linear additive feedback random number generator employing a 61default table of size 31 long integers to return successive pseudo-random 62numbers in the range from 0 to 63.if t 2\u\s731\s10\d\(mi1. 64.if n (2**31)\(mi1. 65The period of this random number generator is very large, approximately 66.if t 16\(mu(2\u\s731\s10\d\(mi1). 67.if n 16*((2**31)\(mi1). 68.Pp 69The 70.Fn random 71and 72.Fn srandom 73functions have (almost) the same calling sequence and initialization properties as the 74.Xr rand 3 75and 76.Xr srand 3 77functions. 78The difference is that 79.Xr rand 3 80produces a much less random sequence \(em in fact, the low dozen bits 81generated by rand go through a cyclic pattern. All the bits generated by 82.Fn random 83are usable. For example, 84.Sq Li random()&01 85will produce a random binary 86value. 87.Pp 88Like 89.Xr rand 3 , 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 srandomdev 100routine initialize a state array using 101.Xr urandom 4 102random number device which returns good random numbers, 103suitable for cryptographic use. 104Note that this particular seeding 105procedure can generate states which are impossible to reproduce by 106calling 107.Fn srandom 108with any value, since the succeeding terms in the 109state buffer are no longer derived from the LC algorithm applied to 110a fixed seed. 111.Pp 112The 113.Fn initstate 114routine allows a state array, passed in as an argument, to be initialized 115for future use. The size of the state array (in bytes) is used by 116.Fn initstate 117to decide how sophisticated a random number generator it should use \(em the 118more state, the better the random numbers will be. 119(Current "optimal" values for the amount of state information are 1208, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 121the nearest known amount. Using less than 8 bytes will cause an error.) 122The seed for the initialization (which specifies a starting point for 123the random number sequence, and provides for restarting at the same 124point) is also an argument. 125The 126.Fn initstate 127function 128returns a pointer to the previous state information array. 129.Pp 130Once a state has been initialized, the 131.Fn setstate 132routine provides for rapid switching between states. 133The 134.Fn setstate 135function 136returns a pointer to the previous state array; its 137argument state array is used for further random number generation 138until the next call to 139.Fn initstate 140or 141.Fn setstate . 142.Pp 143Once a state array has been initialized, it may be restarted at a 144different point either by calling 145.Fn initstate 146(with the desired seed, the state array, and its size) or by calling 147both 148.Fn setstate 149(with the state array) and 150.Fn srandom 151(with the desired seed). 152The advantage of calling both 153.Fn setstate 154and 155.Fn srandom 156is that the size of the state array does not have to be remembered after 157it is initialized. 158.Pp 159With 256 bytes of state information, the period of the random number 160generator is greater than 161.if t 2\u\s769\s10\d, 162.if n 2**69 163which should be sufficient for most purposes. 164.Sh AUTHOR 165Earl T. Cohen 166.Sh DIAGNOSTICS 167If 168.Fn initstate 169is called with less than 8 bytes of state information, or if 170.Fn setstate 171detects that the state information has been garbled, error 172messages are printed on the standard error output. 173.Sh SEE ALSO 174.Xr rand 3 , 175.Xr srand 3 , 176.Xr urandom 4 177.Sh HISTORY 178These 179functions appeared in 180.Bx 4.2 . 181.Sh BUGS 182.Pp 183About 2/3 the speed of 184.Xr rand 3 . 185.Pp 186The historical implementation used to have a very weak seeding; the 187random sequence did not vary much with the seed. 188The current implementation employs a better pseudo-random number 189generator for the initial state calculation. 190