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Neither the name of the University nor the names of its contributors 13.\" may be used to endorse or promote products derived from this software 14.\" without specific prior written permission. 15.\" 16.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 17.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 20.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26.\" SUCH DAMAGE. 27.\" 28.\" @(#)random.3 8.1 (Berkeley) 6/4/93 29.\" $FreeBSD$ 30.\" 31.Dd April 22, 2019 32.Dt RANDOM 3 33.Os 34.Sh NAME 35.Nm random , 36.Nm srandom , 37.Nm srandomdev , 38.Nm initstate , 39.Nm setstate 40.Nd non-cryptographic pseudorandom number generator; routines for changing generators 41.Sh LIBRARY 42.Lb libc 43.Sh SYNOPSIS 44.In stdlib.h 45.Ft long 46.Fn random void 47.Ft void 48.Fn srandom "unsigned int seed" 49.Ft void 50.Fn srandomdev void 51.Ft char * 52.Fn initstate "unsigned int seed" "char *state" "size_t n" 53.Ft char * 54.Fn setstate "char *state" 55.Sh DESCRIPTION 56.Bf -symbolic 57The functions described in this manual page are not secure. 58Applications which require unpredictable random numbers should use 59.Xr arc4random 3 60instead. 61.Ef 62.Pp 63The 64.Fn random 65function 66uses a non-linear additive feedback random number generator employing a 67default table of size 31 long integers to return successive pseudo-random 68numbers in the range from 0 to 69.if t 2\u\s731\s10\d\(mi1. 70.if n (2**31)\(mi1. 71The period of this random number generator is very large, approximately 72.if t 16\(mu(2\u\s731\s10\d\(mi1). 73.if n 16*((2**31)\(mi1). 74.Pp 75The 76.Fn random 77and 78.Fn srandom 79functions have (almost) the same calling sequence and initialization properties as the 80.Xr rand 3 81and 82.Xr srand 3 83functions. 84The difference is that 85.Xr rand 3 86produces a much less random sequence \(em in fact, the low dozen bits 87generated by rand go through a cyclic pattern. 88All the bits generated by 89.Fn random 90are usable. 91For example, 92.Sq Li random()&01 93will produce a random binary 94value. 95.Pp 96Like 97.Xr rand 3 , 98.Fn random 99will by default produce a sequence of numbers that can be duplicated 100by calling 101.Fn srandom 102with 103.Ql 1 104as the seed. 105.Pp 106The 107.Fn srandomdev 108routine initializes a state array using 109pseudo-random numbers obtained from the kernel. 110Note that this particular seeding 111procedure can generate states which are impossible to reproduce by 112calling 113.Fn srandom 114with any value, since the succeeding terms in the 115state buffer are no longer derived from the LC algorithm applied to 116a fixed seed. 117.Pp 118The 119.Fn initstate 120routine allows a state array, passed in as an argument, to be initialized 121for future use. 122The size of the state array (in bytes) is used by 123.Fn initstate 124to decide how sophisticated a random number generator it should use \(em the 125more state, the better the random numbers will be. 126(Current "optimal" values for the amount of state information are 1278, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 128the nearest known amount. 129Using less than 8 bytes will cause an error.) 130The seed for the initialization (which specifies a starting point for 131the random number sequence, and provides for restarting at the same 132point) is also an argument. 133The 134.Fn initstate 135function 136returns a pointer to the previous state information array. 137.Pp 138Once a state has been initialized, the 139.Fn setstate 140routine provides for rapid switching between states. 141The 142.Fn setstate 143function 144returns a pointer to the previous state array; its 145argument state array is used for further random number generation 146until the next call to 147.Fn initstate 148or 149.Fn setstate . 150.Pp 151Once a state array has been initialized, it may be restarted at a 152different point either by calling 153.Fn initstate 154(with the desired seed, the state array, and its size) or by calling 155both 156.Fn setstate 157(with the state array) and 158.Fn srandom 159(with the desired seed). 160The advantage of calling both 161.Fn setstate 162and 163.Fn srandom 164is that the size of the state array does not have to be remembered after 165it is initialized. 166.Pp 167With 256 bytes of state information, the period of the random number 168generator is greater than 169.if t 2\u\s769\s10\d, 170.if n 2**69 171which should be sufficient for most purposes. 172.Sh DIAGNOSTICS 173If 174.Fn initstate 175is called with less than 8 bytes of state information, or if 176.Fn setstate 177detects that the state information has been garbled, 178NULL is returned. 179.Sh SEE ALSO 180.Xr arc4random 3 , 181.Xr lrand48 3 , 182.Xr rand 3 , 183.Xr random 4 184.Sh HISTORY 185These 186functions appeared in 187.Bx 4.2 . 188.Sh AUTHORS 189.An Earl T. Cohen 190