2fe8fb192f
There is important information about booting non-ack images in docs/UPDATING. ack/aout-format images can't be built any more, and booting clang/ELF-format ones is a little different. Updating to the new boot monitor is recommended. Changes in this commit: . drop boot monitor -> allowing dropping ack support . facility to copy ELF boot files to /boot so that old boot monitor can still boot fairly easily, see UPDATING . no more ack-format libraries -> single-case libraries . some cleanup of OBJECT_FMT, COMPILER_TYPE, etc cases . drop several ack toolchain commands, but not all support commands (e.g. aal is gone but acksize is not yet). . a few libc files moved to netbsd libc dir . new /bin/date as minix date used code in libc/ . test compile fix . harmonize includes . /usr/lib is no longer special: without ack, /usr/lib plays no kind of special bootstrapping role any more and bootstrapping is done exclusively through packages, so releases depend even less on the state of the machine making them now. . rename nbsd_lib* to lib* . reduce mtree
183 lines
5.3 KiB
Groff
183 lines
5.3 KiB
Groff
.\" $NetBSD: random.3,v 1.19 2008/02/28 16:16:35 christos Exp $
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.\"
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.\" Copyright (c) 1983, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" from: @(#)random.3 8.1 (Berkeley) 6/4/93
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.\"
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.Dd February 28, 2008
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.Dt RANDOM 3
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.Os
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.Sh NAME
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.Nm random ,
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.Nm srandom ,
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.Nm initstate ,
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.Nm setstate
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.Nd better random number generator; routines for changing generators
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.Sh LIBRARY
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.Lb libc
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.Sh SYNOPSIS
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.In stdlib.h
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.Ft long
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.Fn random void
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.Ft void
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.Fn srandom "unsigned long seed"
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.Ft char *
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.Fn initstate "unsigned long seed" "char *state" "size_t n"
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.Ft char *
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.Fn setstate "char *state"
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.Sh DESCRIPTION
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The
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.Fn random
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function
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uses a non-linear additive feedback random number generator employing a
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default table of size 31 long integers to return successive pseudo-random
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numbers in the range from 0 to
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.if t 2\u\s731\s10\d\(mi1.
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.if n (2**31)\(mi1.
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The period of this random number generator is very large, approximately
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.if t 16\(mu(2\u\s731\s10\d\(mi1).
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.if n 16*((2**31)\(mi1).
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The maximum value
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.Dv RANDOM_MAX
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is defined in
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.In stdlib.h .
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.Pp
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The
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.Fn random
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and
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.Fn srandom
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have (almost) the same calling sequence and initialization properties as
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.Xr rand 3
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and
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.Xr srand 3 .
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The difference is that
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.Xr rand 3
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produces a much less random sequence \(em in fact, the low dozen bits
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generated by
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.Xr rand 3
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go through a cyclic pattern.
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All the bits generated by
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.Fn random
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are usable.
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For example,
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.Sq Li random()\*[Am]01
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will produce a random binary value.
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.Pp
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Like
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.Xr rand 3 ,
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.Fn random
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will by default produce a sequence of numbers that can be duplicated
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by calling
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.Fn srandom
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with
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.Ql 1
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as the seed.
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.Pp
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The
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.Fn initstate
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routine allows a state array, passed in as an argument, to be initialized
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for future use.
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The size of the state array (in bytes) is used by
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.Fn initstate
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to decide how sophisticated a random number generator it should use \(em the
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more state, the better the random numbers will be.
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(Current "optimal" values for the amount of state information are
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8, 32, 64, 128, and 256 bytes; other amounts will be rounded down to
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the nearest known amount.
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Using less than 8 bytes will cause an error).
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The seed for the initialization (which specifies a starting point for
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the random number sequence, and provides for restarting at the same
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point) is also an argument.
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The state array passed to
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.Fn initstate
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must be aligned to a 32-bit boundary.
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This can be achieved by using
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a suitably-sized array of ints, and casting the array to char * when
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passing it to
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.Fn initstate .
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The
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.Fn initstate
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function
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returns a pointer to the previous state information array.
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.Pp
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Once a state has been initialized, the
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.Fn setstate
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routine provides for rapid switching between states.
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The
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.Fn setstate
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function
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returns a pointer to the previous state array; its
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argument state array is used for further random number generation
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until the next call to
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.Fn initstate
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or
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.Fn setstate .
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.Pp
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Once a state array has been initialized, it may be restarted at a
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different point either by calling
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.Fn initstate
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(with the desired seed, the state array, and its size) or by calling
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both
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.Fn setstate
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(with the state array) and
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.Fn srandom
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(with the desired seed).
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The advantage of calling both
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.Fn setstate
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and
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.Fn srandom
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is that the size of the state array does not have to be remembered after
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it is initialized.
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.Pp
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With 256 bytes of state information, the period of the random number
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generator is greater than
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.if t 2\u\s769\s10\d,
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.if n 2**69
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which should be sufficient for most purposes.
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.Sh DIAGNOSTICS
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If
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.Fn initstate
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is called with less than 8 bytes of state information, or if
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.Fn setstate
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detects that the state information has been garbled, error
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messages are printed on the standard error output.
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.Sh SEE ALSO
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.Xr rand 3 ,
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.Xr srand 3 ,
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.Xr rnd 4 ,
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.Xr rnd 9
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.Sh HISTORY
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These
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functions appeared in
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.Bx 4.2 .
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.Sh AUTHORS
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.An Earl T. Cohen
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.Sh BUGS
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About 2/3 the speed of
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.Xr rand 3 .
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