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author | wollman <wollman@FreeBSD.org> | 1994-09-23 00:37:55 +0000 |
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committer | wollman <wollman@FreeBSD.org> | 1994-09-23 00:37:55 +0000 |
commit | 4c045ca123398a5109e2d35cf6cbfb3c2bb9df93 (patch) | |
tree | 765891a14c11280bc539082a7de5e9dd7846bb99 /lib/libc/gen/rand48.3 | |
parent | eed32da9d43503cb4e88bc1ce7ca4ab638214d91 (diff) | |
download | FreeBSD-src-4c045ca123398a5109e2d35cf6cbfb3c2bb9df93.zip FreeBSD-src-4c045ca123398a5109e2d35cf6cbfb3c2bb9df93.tar.gz |
Added *ran48 functions, and put them in the correct place this time.
Obtained from: 1.1.5
Diffstat (limited to 'lib/libc/gen/rand48.3')
-rw-r--r-- | lib/libc/gen/rand48.3 | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/lib/libc/gen/rand48.3 b/lib/libc/gen/rand48.3 new file mode 100644 index 0000000..176303d --- /dev/null +++ b/lib/libc/gen/rand48.3 @@ -0,0 +1,160 @@ +\" Copyright (c) 1993 Martin Birgmeier +.\" All rights reserved. +.\" +.\" You may redistribute unmodified or modified versions of this source +.\" code provided that the above copyright notice and this and the +.\" following conditions are retained. +.\" +.\" This software is provided ``as is'', and comes with no warranties +.\" of any kind. I shall in no event be liable for anything that happens +.\" to anyone/anything when using this software. +.\" +.\" @(#)rand48.3 V1.0 MB 8 Oct 1993 +.\" +.Dd October 8, 1993 +.Dt RAND48 3 +.Os FreeBSD +.Sh NAME +.Nm drand48 , +.Nm erand48 , +.Nm lrand48 , +.Nm nrand48 , +.Nm mrand48 , +.Nm jrand48 , +.Nm srand48 , +.Nm seed48 , +.Nm lcong48 +.Nd pseudo random number generators and initialization routines +.Sh SYNOPSIS +.Fd #include <stdlib.h> +.Ft double +.Fn drand48 void +.Ft double +.Fn erand48 "unsigned short xseed[3]" +.Ft long +.Fn lrand48 void +.Ft long +.Fn nrand48 "unsigned short xseed[3]" +.Ft long +.Fn mrand48 void +.Ft long +.Fn jrand48 "unsigned short xseed[3]" +.Ft void +.Fn srand48 "long seed" +.Ft "unsigned short *" +.Fn seed48 "unsigned short xseed[3]" +.Ft void +.Fn lcong48 "unsigned short p[7]" +.Sh DESCRIPTION +The +.Fn rand48 +family of functions generates pseudo-random numbers using a linear +congruential algorithm working on integers 48 bits in size. The +particular formula employed is +r(n+1) = (a * r(n) + c) mod m +where the default values are +for the multiplicand a = 0xfdeece66d = 25214903917 and +the addend c = 0xb = 11. The modul is always fixed at m = 2 ** 48. +r(n) is called the seed of the random number generator. +.Pp +For all the six generator routines described next, the first +computational step is to perform a single iteration of the algorithm. +.Pp +.Fn drand48 +and +.Fn erand48 +return values of type double. The full 48 bits of r(n+1) are +loaded into the mantissa of the returned value, with the exponent set +such that the values produced lie in the interval [0.0, 1.0). +.Pp +.Fn lrand48 +and +.Fn nrand48 +return values of type long in the range +[-2**31, 2**31-1]. The high-order (32) bits of +r(n+1) are loaded into the returned value. +.Pp +.Fn mrand48 +and +.Fn jrand48 +return values of type long in the range +[0, 2**31-1]. The high-order (31) bits of +r(n+1) are loaded into the lower bits of the returned value, with +the topmost (sign) bit set to zero. +.Pp +.Fn drand48 , +.Fn lrand48 , +and +.Fn mrand48 +use an internal buffer to store r(n). For these functions +the initial value of r(0) = 0x1234abcd330e = 20017429951246. +.Pp +On the other hand, +.Fn erand48 , +.Fn nrand48 , +and +.Fn jrand48 +use a user-supplied buffer to store the seed r(n), +which consists of an array of 3 shorts, where the zeroth member +holds the least significant bits. +.Pp +All functions share the same multiplicand and addend. +.Pp +.Fn srand48 +is used to initialize the internal buffer r(n) of +.Fn drand48 , +.Fn lrand48 , +and +.Fn mrand48 +such that the 32 bits of the seed value are copied into the upper 32 bits +of r(n), with the lower 16 bits of r(n) arbitrarily being set to 0x330e. +Additionally, the constant multiplicand and addend of the algorithm are +reset to the default values given above. +.Pp +.Fn seed48 +also initializes the internal buffer r(n) of +.Fn drand48 , +.Fn lrand48 , +and +.Fn mrand48 , +but here all 48 bits of the seed can be specified in an array of 3 shorts, +where the zeroth member specifies the lowest bits. Again, +the constant multiplicand and addend of the algorithm are +reset to the default values given above. +.Fn seed48 +returns a pointer to an array of 3 shorts which contains the old seed. +This array is statically allocated, thus its contents are lost after +each new call to +.Fn seed48 . +.Pp +Finally, +.Fn lcong48 +allows full control over the multiplicand and addend used in +.Fn drand48 , +.Fn erand48 , +.Fn lrand48 , +.Fn nrand48 , +.Fn mrand48 , +and +.Fn jrand48 , +and the seed used in +.Fn drand48 , +.Fn lrand48 , +and +.Fn mrand48 . +An array of 7 shorts is passed as parameter; the first three shorts are +used to initialize the seed; the second three are used to initialize the +multiplicand; and the last short is used to initialize the addend. +It is thus not possible to use values greater than 0xffff as the addend. +.Pp +Note that all three methods of seeding the random number generator +always also set the multiplicand and addend for any of the six +generator calls. +.Pp +For a more powerful random number generator, see +.Xr random 3 +.Sh AUTHOR +Martin Birgmeier +.Sh SEE ALSO +.Xr rand 3 , +.Xr random 3 . |