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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 January 20, 2020 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 63Unless initialized with less than 32 bytes of state, the 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 75If initialized with less than 32 bytes of state, 76.Fn random 77uses the same poor-quality Park-Miller LCG as 78.Xr rand 3 . 79.Pp 80The 81.Fn random 82and 83.Fn srandom 84functions are analagous to 85.Xr rand 3 86and 87.Xr srand 3 . 88The difference is that 89.Xr rand 3 90is a worse pseudo-random number generator. 91.Pp 92Like 93.Xr rand 3 , 94.Fn random 95is implicitly initialized as if 96.Fn srandom "1" 97had been invoked explicitly. 98.Pp 99The 100.Fn srandomdev 101routine initializes the state array using random numbers obtained from the 102kernel. 103This can generate states which are impossible to reproduce by calling 104.Fn srandom , 105because the succeeding terms in the state buffer are no longer derived from the 106Park-Miller LCG algorithm applied to a fixed seed. 107.Pp 108The 109.Fn initstate 110routine initializes the provided state array of 111.Vt uint32_t 112values and uses it in future 113.Fn random 114invocations. 115(Despite the 116.Vt char * 117type of 118.Fa state , 119the underlying object must be a naturally aligned array of 32-bit values.) 120The size of the state array (in bytes) is used by 121.Fn initstate 122to decide how sophisticated a random number generator it should use \(em the 123more state, the better the random numbers will be. 124(Current "optimal" values for the amount of state information are 1258, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 126the nearest known amount. 127Using less than 8 bytes will cause an error.) 128The 129.Fa seed 130is used as in 131.Fn srandom . 132The 133.Fn initstate 134function 135returns a pointer to the previous state information array. 136.Pp 137The 138.Fn setstate 139routine switches 140.Fn random 141to using the provided state. 142It returns a pointer to the previous state. 143.Pp 144Once a state array has been initialized, it may be restarted at a 145different point either by calling 146.Fn initstate 147(with the desired seed, the state array, and its size) or by calling 148both 149.Fn setstate 150(with the state array) and 151.Fn srandom 152(with the desired seed). 153The advantage of calling both 154.Fn setstate 155and 156.Fn srandom 157is that the size of the state array does not have to be remembered after 158it is initialized. 159.Pp 160With 256 bytes of state information, the period of the random number 161generator is greater than 162.if t 2\u\s769\s10\d, 163.if n 2**69 164which should be sufficient for most purposes. 165.Sh DIAGNOSTICS 166If 167.Fn initstate 168is called with less than 8 bytes of state information, or if 169.Fn setstate 170detects that the state information has been garbled, 171NULL is returned. 172.Sh SEE ALSO 173.Xr arc4random 3 , 174.Xr lrand48 3 , 175.Xr rand 3 , 176.Xr random 4 177.Sh HISTORY 178These 179functions appeared in 180.Bx 4.2 . 181.Sh AUTHORS 182.An Earl T. Cohen 183