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
164 lines
4.4 KiB
Groff
164 lines
4.4 KiB
Groff
.\" $NetBSD: rand48.3,v 1.11 2006/03/31 11:43:54 drochner Exp $
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.\"
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.\" Copyright (c) 1993 Martin Birgmeier
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.\" All rights reserved.
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.\"
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.\" You may redistribute unmodified or modified versions of this source
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.\" code provided that the above copyright notice and this and the
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.\" following conditions are retained.
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.\"
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.\" This software is provided ``as is'', and comes with no warranties
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.\" of any kind. I shall in no event be liable for anything that happens
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.\" to anyone/anything when using this software.
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.\"
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.Dd October 8, 1993
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.Dt RAND48 3
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.Os
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.Sh NAME
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.Nm drand48 ,
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.Nm erand48 ,
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.Nm lrand48 ,
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.Nm nrand48 ,
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.Nm mrand48 ,
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.Nm jrand48 ,
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.Nm srand48 ,
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.Nm seed48 ,
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.Nm lcong48
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.Nd pseudo-random number generators and initialization routines
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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 double
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.Fn drand48 void
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.Ft double
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.Fn erand48 "unsigned short xseed[3]"
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.Ft long
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.Fn lrand48 void
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.Ft long
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.Fn nrand48 "unsigned short xseed[3]"
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.Ft long
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.Fn mrand48 void
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.Ft long
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.Fn jrand48 "unsigned short xseed[3]"
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.Ft void
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.Fn srand48 "long seed"
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.Ft "unsigned short *"
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.Fn seed48 "unsigned short xseed[3]"
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.Ft void
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.Fn lcong48 "unsigned short p[7]"
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.Sh DESCRIPTION
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The
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.Fn rand48
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family of functions generates pseudo-random numbers using a linear
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congruential algorithm working on integers 48 bits in size.
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The particular formula employed is
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r(n+1) = (a * r(n) + c) mod m
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where the default values are
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for the multiplicand a = 0x5deece66d = 25214903917 and
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the addend c = 0xb = 11.
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The modulus is always fixed at m = 2 ** 48.
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r(n) is called the seed of the random number generator.
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.Pp
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For all the six generator routines described next, the first
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computational step is to perform a single iteration of the algorithm.
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.Pp
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.Fn drand48
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and
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.Fn erand48
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return values of type double.
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The full 48 bits of r(n+1) are loaded into the mantissa of the
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returned value, with the exponent set such that the values produced
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lie in the interval [0.0, 1.0).
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.Pp
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.Fn lrand48
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and
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.Fn nrand48
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return values of type long in the range [0, 2**31-1].
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The high-order (31) bits of r(n+1) are loaded into the lower bits
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of the returned value, with the topmost (sign) bit set to zero.
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.Pp
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.Fn mrand48
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and
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.Fn jrand48
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return values of type long in the range [-2**31, 2**31-1].
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The high-order (32) bits of r(n+1) are loaded into the returned value.
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.Pp
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.Fn drand48 ,
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.Fn lrand48 ,
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and
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.Fn mrand48
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use an internal buffer to store r(n).
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For these functions
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the initial value of r(0) = 0x1234abcd330e = 20017429951246.
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.Pp
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On the other hand,
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.Fn erand48 ,
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.Fn nrand48 ,
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and
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.Fn jrand48
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use a user-supplied buffer to store the seed r(n), which consists
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of an array of 3 shorts, where the zeroth member holds the least
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significant bits.
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.Pp
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All functions share the same multiplicand and addend.
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.Pp
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.Fn srand48
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is used to initialize the internal buffer r(n) of
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.Fn drand48 ,
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.Fn lrand48 ,
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and
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.Fn mrand48
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such that the 32 bits of the seed value are copied into the upper 32 bits
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of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e.
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Additionally, the constant multiplicand and addend of the algorithm are
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reset to the default values given above.
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.Pp
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.Fn seed48
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also initializes the internal buffer r(n) of
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.Fn drand48 ,
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.Fn lrand48 ,
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and
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.Fn mrand48 ,
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but here all 48 bits of the seed can be specified in an array of 3 shorts,
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where the zeroth member specifies the lowest bits.
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Again, the constant multiplicand and addend of the algorithm are
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reset to the default values given above.
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.Fn seed48
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returns a pointer to an array of 3 shorts which contains the old seed.
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This array is statically allocated, thus its contents are lost after
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each new call to
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.Fn seed48 .
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.Pp
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Finally,
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.Fn lcong48
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allows full control over the multiplicand and addend used in
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.Fn drand48 ,
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.Fn erand48 ,
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.Fn lrand48 ,
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.Fn nrand48 ,
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.Fn mrand48 ,
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and
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.Fn jrand48 ,
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and the seed used in
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.Fn drand48 ,
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.Fn lrand48 ,
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and
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.Fn mrand48 .
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An array of 7 shorts is passed as parameter; the first three shorts are
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used to initialize the seed; the second three are used to initialize the
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multiplicand; and the last short is used to initialize the addend.
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It is thus not possible to use values greater than 0xffff as the addend.
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.Pp
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Note that all three methods of seeding the random number generator
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always also set the multiplicand and addend for any of the six
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generator calls.
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.Pp
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For a more powerful random number generator, see
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.Xr random 3 .
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.Sh SEE ALSO
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.Xr rand 3 ,
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.Xr random 3
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.Sh AUTHORS
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Martin Birgmeier
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