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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 February 1, 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 poor-quality 32-bit Park-Miller LCG. 78.Pp 79The 80.Fn random 81and 82.Fn srandom 83functions are analagous to 84.Xr rand 3 85and 86.Xr srand 3 . 87.Pp 88Like 89.Xr rand 3 , 90.Fn random 91is implicitly initialized as if 92.Fn srandom "1" 93had been invoked explicitly. 94.Pp 95The 96.Fn srandomdev 97routine initializes the state array using random numbers obtained from the 98kernel. 99This can generate states which are impossible to reproduce by calling 100.Fn srandom , 101because the succeeding terms in the state buffer are no longer derived from the 102Park-Miller LCG algorithm applied to a fixed seed. 103.Pp 104The 105.Fn initstate 106routine initializes the provided state array of 107.Vt uint32_t 108values and uses it in future 109.Fn random 110invocations. 111(Despite the 112.Vt char * 113type of 114.Fa state , 115the underlying object must be a naturally aligned array of 32-bit values.) 116The size of the state array (in bytes) is used by 117.Fn initstate 118to decide how sophisticated a random number generator it should use \(em the 119more state, the better the random numbers will be. 120(Current "optimal" values for the amount of state information are 1218, 32, 64, 128, and 256 bytes; other amounts will be rounded down to 122the nearest known amount. 123Using less than 8 bytes will cause an error.) 124The 125.Fa seed 126is used as in 127.Fn srandom . 128The 129.Fn initstate 130function 131returns a pointer to the previous state information array. 132.Pp 133The 134.Fn setstate 135routine switches 136.Fn random 137to using the provided state. 138It returns a pointer to the previous state. 139.Pp 140Once a state array has been initialized, it may be restarted at a 141different point either by calling 142.Fn initstate 143(with the desired seed, the state array, and its size) or by calling 144both 145.Fn setstate 146(with the state array) and 147.Fn srandom 148(with the desired seed). 149The advantage of calling both 150.Fn setstate 151and 152.Fn srandom 153is that the size of the state array does not have to be remembered after 154it is initialized. 155.Pp 156With 256 bytes of state information, the period of the random number 157generator is greater than 158.if t 2\u\s769\s10\d, 159.if n 2**69 160which should be sufficient for most purposes. 161.Sh DIAGNOSTICS 162If 163.Fn initstate 164is called with less than 8 bytes of state information, or if 165.Fn setstate 166detects that the state information has been garbled, 167NULL is returned. 168.Sh SEE ALSO 169.Xr arc4random 3 , 170.Xr lrand48 3 , 171.Xr rand 3 , 172.Xr random 4 173.Sh HISTORY 174These 175functions appeared in 176.Bx 4.2 . 177.Sh AUTHORS 178.An Earl T. Cohen 179