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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.Dd February 1, 2020 29.Dt RANDOM 3 30.Os 31.Sh NAME 32.Nm random , 33.Nm srandom , 34.Nm srandomdev , 35.Nm initstate , 36.Nm setstate 37.Nd non-cryptographic pseudorandom number generator; routines for changing generators 38.Sh LIBRARY 39.Lb libc 40.Sh SYNOPSIS 41.In stdlib.h 42.Ft long 43.Fn random void 44.Ft void 45.Fn srandom "unsigned int seed" 46.Ft void 47.Fn srandomdev void 48.Ft char * 49.Fn initstate "unsigned int seed" "char *state" "size_t n" 50.Ft char * 51.Fn setstate "char *state" 52.Sh DESCRIPTION 53.Bf -symbolic 54The functions described in this manual page are not secure. 55Applications which require unpredictable random numbers should use 56.Xr arc4random 3 57instead. 58.Ef 59.Pp 60Unless initialized with less than 32 bytes of state, the 61.Fn random 62function 63uses a non-linear additive feedback random number generator employing a 64default table of size 31 long integers to return successive pseudo-random 65numbers in the range from 0 to 66.if t 2\u\s731\s10\d\(mi1. 67.if n (2**31)\(mi1. 68The period of this random number generator is very large, approximately 69.if t 16\(mu(2\u\s731\s10\d\(mi1). 70.if n 16*((2**31)\(mi1). 71.Pp 72If initialized with less than 32 bytes of state, 73.Fn random 74uses the poor-quality 32-bit Park-Miller LCG. 75.Pp 76The 77.Fn random 78and 79.Fn srandom 80functions are analagous to 81.Xr rand 3 82and 83.Xr srand 3 . 84.Pp 85Like 86.Xr rand 3 , 87.Fn random 88is implicitly initialized as if 89.Fn srandom "1" 90had been invoked explicitly. 91.Pp 92The 93.Fn srandomdev 94routine initializes the state array using random numbers obtained from the 95kernel. 96This can generate states which are impossible to reproduce by calling 97.Fn srandom , 98because the succeeding terms in the state buffer are no longer derived from the 99Park-Miller LCG algorithm applied to a fixed seed. 100.Pp 101The 102.Fn initstate 103routine initializes the provided state array of 104.Vt uint32_t 105values and uses it in future 106.Fn random 107invocations. 108(Despite the 109.Vt char * 110type of 111.Fa state , 112the underlying object must be a naturally aligned array of 32-bit values.) 113The size of the state array (in bytes) is used by 114.Fn initstate 115to decide how sophisticated a random number generator it should use \(em the 116more state, the better the random numbers will be. 117(Current "optimal" values for the amount of state information are 1188, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 119the nearest known amount. 120Using less than 8 bytes will cause an error.) 121The 122.Fa seed 123is used as in 124.Fn srandom . 125The 126.Fn initstate 127function 128returns a pointer to the previous state information array. 129.Pp 130The 131.Fn setstate 132routine switches 133.Fn random 134to using the provided state. 135It returns a pointer to the previous state. 136.Pp 137Once a state array has been initialized, it may be restarted at a 138different point either by calling 139.Fn initstate 140(with the desired seed, the state array, and its size) or by calling 141both 142.Fn setstate 143(with the state array) and 144.Fn srandom 145(with the desired seed). 146The advantage of calling both 147.Fn setstate 148and 149.Fn srandom 150is that the size of the state array does not have to be remembered after 151it is initialized. 152.Pp 153With 256 bytes of state information, the period of the random number 154generator is greater than 155.if t 2\u\s769\s10\d, 156.if n 2**69 157which should be sufficient for most purposes. 158.Sh DIAGNOSTICS 159If 160.Fn initstate 161is called with less than 8 bytes of state information, or if 162.Fn setstate 163detects that the state information has been garbled, 164NULL is returned. 165.Sh SEE ALSO 166.Xr arc4random 3 , 167.Xr lrand48 3 , 168.Xr rand 3 , 169.Xr random 4 170.Sh HISTORY 171These 172functions appeared in 173.Bx 4.2 . 174.Sh AUTHORS 175.An Earl T. Cohen 176