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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.\" 30.Dd February 1, 2020 31.Dt RANDOM 3 32.Os 33.Sh NAME 34.Nm random , 35.Nm srandom , 36.Nm srandomdev , 37.Nm initstate , 38.Nm setstate 39.Nd non-cryptographic pseudorandom number generator; routines for changing generators 40.Sh LIBRARY 41.Lb libc 42.Sh SYNOPSIS 43.In stdlib.h 44.Ft long 45.Fn random void 46.Ft void 47.Fn srandom "unsigned int seed" 48.Ft void 49.Fn srandomdev void 50.Ft char * 51.Fn initstate "unsigned int seed" "char *state" "size_t n" 52.Ft char * 53.Fn setstate "char *state" 54.Sh DESCRIPTION 55.Bf -symbolic 56The functions described in this manual page are not secure. 57Applications which require unpredictable random numbers should use 58.Xr arc4random 3 59instead. 60.Ef 61.Pp 62Unless initialized with less than 32 bytes of state, the 63.Fn random 64function 65uses a non-linear additive feedback random number generator employing a 66default table of size 31 long integers to return successive pseudo-random 67numbers in the range from 0 to 68.if t 2\u\s731\s10\d\(mi1. 69.if n (2**31)\(mi1. 70The period of this random number generator is very large, approximately 71.if t 16\(mu(2\u\s731\s10\d\(mi1). 72.if n 16*((2**31)\(mi1). 73.Pp 74If initialized with less than 32 bytes of state, 75.Fn random 76uses the poor-quality 32-bit Park-Miller LCG. 77.Pp 78The 79.Fn random 80and 81.Fn srandom 82functions are analagous to 83.Xr rand 3 84and 85.Xr srand 3 . 86.Pp 87Like 88.Xr rand 3 , 89.Fn random 90is implicitly initialized as if 91.Fn srandom "1" 92had been invoked explicitly. 93.Pp 94The 95.Fn srandomdev 96routine initializes the state array using random numbers obtained from the 97kernel. 98This can generate states which are impossible to reproduce by calling 99.Fn srandom , 100because the succeeding terms in the state buffer are no longer derived from the 101Park-Miller LCG algorithm applied to a fixed seed. 102.Pp 103The 104.Fn initstate 105routine initializes the provided state array of 106.Vt uint32_t 107values and uses it in future 108.Fn random 109invocations. 110(Despite the 111.Vt char * 112type of 113.Fa state , 114the underlying object must be a naturally aligned array of 32-bit values.) 115The 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. 122Using less than 8 bytes will cause an error.) 123The 124.Fa seed 125is used as in 126.Fn srandom . 127The 128.Fn initstate 129function 130returns a pointer to the previous state information array. 131.Pp 132The 133.Fn setstate 134routine switches 135.Fn random 136to using the provided state. 137It returns a pointer to the previous state. 138.Pp 139Once a state array has been initialized, it may be restarted at a 140different point either by calling 141.Fn initstate 142(with the desired seed, the state array, and its size) or by calling 143both 144.Fn setstate 145(with the state array) and 146.Fn srandom 147(with the desired seed). 148The advantage of calling both 149.Fn setstate 150and 151.Fn srandom 152is that the size of the state array does not have to be remembered after 153it is initialized. 154.Pp 155With 256 bytes of state information, the period of the random number 156generator is greater than 157.if t 2\u\s769\s10\d, 158.if n 2**69 159which should be sufficient for most purposes. 160.Sh DIAGNOSTICS 161If 162.Fn initstate 163is called with less than 8 bytes of state information, or if 164.Fn setstate 165detects that the state information has been garbled, 166NULL is returned. 167.Sh SEE ALSO 168.Xr arc4random 3 , 169.Xr lrand48 3 , 170.Xr rand 3 , 171.Xr random 4 172.Sh HISTORY 173These 174functions appeared in 175.Bx 4.2 . 176.Sh AUTHORS 177.An Earl T. Cohen 178