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Diffstat (limited to 'lib/libc/stdlib/random.3')
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diff --git a/lib/libc/stdlib/random.3 b/lib/libc/stdlib/random.3 new file mode 100644 index 000000000000..b29536d4371d --- /dev/null +++ b/lib/libc/stdlib/random.3 @@ -0,0 +1,175 @@ +.\" Copyright (c) 1983, 1991, 1993 +.\" The Regents of the University of California. All rights reserved. +.\" +.\" Redistribution and use in source and binary forms, with or without +.\" modification, are permitted provided that the following conditions +.\" are met: +.\" 1. Redistributions of source code must retain the above copyright +.\" notice, this list of conditions and the following disclaimer. +.\" 2. Redistributions in binary form must reproduce the above copyright +.\" notice, this list of conditions and the following disclaimer in the +.\" documentation and/or other materials provided with the distribution. +.\" 3. Neither the name of the University nor the names of its contributors +.\" may be used to endorse or promote products derived from this software +.\" without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND +.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE +.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE +.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE +.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL +.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS +.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) +.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY +.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF +.\" SUCH DAMAGE. +.\" +.Dd February 1, 2020 +.Dt RANDOM 3 +.Os +.Sh NAME +.Nm random , +.Nm srandom , +.Nm srandomdev , +.Nm initstate , +.Nm setstate +.Nd non-cryptographic pseudorandom number generator; routines for changing generators +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In stdlib.h +.Ft long +.Fn random void +.Ft void +.Fn srandom "unsigned int seed" +.Ft void +.Fn srandomdev void +.Ft char * +.Fn initstate "unsigned int seed" "char *state" "size_t n" +.Ft char * +.Fn setstate "char *state" +.Sh DESCRIPTION +.Bf -symbolic +The functions described in this manual page are not secure. +Applications which require unpredictable random numbers should use +.Xr arc4random 3 +instead. +.Ef +.Pp +Unless initialized with less than 32 bytes of state, the +.Fn random +function +uses a non-linear additive feedback random number generator employing a +default table of size 31 long integers to return successive pseudo-random +numbers in the range from 0 to +.if t 2\u\s731\s10\d\(mi1. +.if n (2**31)\(mi1. +The period of this random number generator is very large, approximately +.if t 16\(mu(2\u\s731\s10\d\(mi1). +.if n 16*((2**31)\(mi1). +.Pp +If initialized with less than 32 bytes of state, +.Fn random +uses the poor-quality 32-bit Park-Miller LCG. +.Pp +The +.Fn random +and +.Fn srandom +functions are analagous to +.Xr rand 3 +and +.Xr srand 3 . +.Pp +Like +.Xr rand 3 , +.Fn random +is implicitly initialized as if +.Fn srandom "1" +had been invoked explicitly. +.Pp +The +.Fn srandomdev +routine initializes the state array using random numbers obtained from the +kernel. +This can generate states which are impossible to reproduce by calling +.Fn srandom , +because the succeeding terms in the state buffer are no longer derived from the +Park-Miller LCG algorithm applied to a fixed seed. +.Pp +The +.Fn initstate +routine initializes the provided state array of +.Vt uint32_t +values and uses it in future +.Fn random +invocations. +(Despite the +.Vt char * +type of +.Fa state , +the underlying object must be a naturally aligned array of 32-bit values.) +The size of the state array (in bytes) is used by +.Fn initstate +to decide how sophisticated a random number generator it should use \(em the +more state, the better the random numbers will be. +(Current "optimal" values for the amount of state information are +8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to +the nearest known amount. +Using less than 8 bytes will cause an error.) +The +.Fa seed +is used as in +.Fn srandom . +The +.Fn initstate +function +returns a pointer to the previous state information array. +.Pp +The +.Fn setstate +routine switches +.Fn random +to using the provided state. +It returns a pointer to the previous state. +.Pp +Once a state array has been initialized, it may be restarted at a +different point either by calling +.Fn initstate +(with the desired seed, the state array, and its size) or by calling +both +.Fn setstate +(with the state array) and +.Fn srandom +(with the desired seed). +The advantage of calling both +.Fn setstate +and +.Fn srandom +is that the size of the state array does not have to be remembered after +it is initialized. +.Pp +With 256 bytes of state information, the period of the random number +generator is greater than +.if t 2\u\s769\s10\d, +.if n 2**69 +which should be sufficient for most purposes. +.Sh DIAGNOSTICS +If +.Fn initstate +is called with less than 8 bytes of state information, or if +.Fn setstate +detects that the state information has been garbled, +NULL is returned. +.Sh SEE ALSO +.Xr arc4random 3 , +.Xr lrand48 3 , +.Xr rand 3 , +.Xr random 4 +.Sh HISTORY +These +functions appeared in +.Bx 4.2 . +.Sh AUTHORS +.An Earl T. Cohen |