.\" to anyone/anything when using this software.
.\"
.\" @(#)rand48.3 V1.0 MB 8 Oct 1993
-.\" $FreeBSD: src/lib/libc/gen/rand48.3,v 1.13 2001/10/01 16:08:51 ru Exp $
+.\" $FreeBSD: src/lib/libc/gen/rand48.3,v 1.16 2004/07/02 23:52:10 ru Exp $
.\"
.Dd October 8, 1993
.Dt RAND48 3
.Sh NAME
.Nm drand48 ,
.Nm erand48 ,
+.Nm jrand48 ,
+.Nm lcong48 ,
.Nm lrand48 ,
-.Nm nrand48 ,
.Nm mrand48 ,
-.Nm jrand48 ,
-.Nm srand48 ,
+.Nm nrand48 ,
.Nm seed48 ,
-.Nm lcong48
+.Nm srand48
.Nd pseudo random number generators and initialization routines
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In stdlib.h
.Ft double
-.Fn drand48 void
+.Fo drand48
+.Fa void
+.Fc
.Ft double
-.Fn erand48 "unsigned short xseed[3]"
+.Fo erand48
+.Fa "unsigned short xsubi[3]"
+.Fc
.Ft long
-.Fn lrand48 void
+.Fo jrand48
+.Fa "unsigned short xsubi[3]"
+.Fc
+.Ft void
+.Fo lcong48
+.Fa "unsigned short param[7]"
+.Fc
.Ft long
-.Fn nrand48 "unsigned short xseed[3]"
+.Fo lrand48
+.Fa void
+.Fc
.Ft long
-.Fn mrand48 void
+.Fo mrand48
+.Fa void
+.Fc
.Ft long
-.Fn jrand48 "unsigned short xseed[3]"
-.Ft void
-.Fn srand48 "long seed"
+.Fo nrand48
+.Fa "unsigned short xsubi[3]"
+.Fc
.Ft "unsigned short *"
-.Fn seed48 "unsigned short xseed[3]"
+.Fo seed48
+.Fa "unsigned short seed16v[3]"
+.Fc
.Ft void
-.Fn lcong48 "unsigned short p[7]"
+.Fo srand48
+.Fa "long seedval"
+.Fc
.Sh DESCRIPTION
The
.Fn rand48
-family of functions generates pseudo-random numbers using a linear
+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.
+r(n+1) = (a * r(n) + c) mod m.
+The default value for the multiplicand `a' is 0xfdeece66d (25214903917).
+The default value for the the addend `c' is 0xb (11).
The modulo 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
+For the six generator routines described next, the first
computational step is to perform a single iteration of the algorithm.
.Pp
+The
.Fn drand48
and
.Fn erand48
+functions
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
+The
.Fn lrand48
and
.Fn nrand48
+functions
return values of type long in the range
-[0, 2**31-1]. The high-order (31) bits of
+[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
+The
.Fn mrand48
and
.Fn jrand48
+functions
return values of type long in the range
-[-2**31, 2**31-1]. The high-order (32) bits of
+[-2**31, 2**31-1].
+The high-order (32) bits of
r(n+1) are loaded into the returned value.
.Pp
+The
.Fn drand48 ,
.Fn lrand48 ,
and
.Fn mrand48
-use an internal buffer to store r(n). For these functions
+functions
+use an internal buffer to store r(n).
+For these functions
the initial value of r(0) = 0x1234abcd330e = 20017429951246.
.Pp
On the other hand,
.Pp
All functions share the same multiplicand and addend.
.Pp
+The
.Fn srand48
+function
is used to initialize the internal buffer r(n) of
.Fn drand48 ,
.Fn lrand48 ,
and
-.Fn mrand48
+.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
+The
.Fn seed48
+function
also initializes the internal buffer r(n) of
.Fn drand48 ,
.Fn lrand48 ,
Again,
the constant multiplicand and addend of the algorithm are
reset to the default values given above.
+The
.Fn seed48
+function
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
+This array is statically allocated; thus, its contents are lost after
each new call to
.Fn seed48 .
.Pp
.Fn lrand48 ,
and
.Fn mrand48 .
-An array of 7 shorts is passed as parameter; the first three shorts are
+An array of 7 shorts is passed as argument; 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.
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