@ -9,9 +9,9 @@
.\" of any kind. I shall in no event be liable for anything that happens
.\" to anyone/anything when using this software.
.\"
.\" $OpenBSD: rand48.3,v 1.16 2014/11/25 17:26:34 miller t Exp $
.\" $OpenBSD: rand48.3,v 1.17 2014/12/08 21:45:20 deraad t Exp $
.\"
.Dd $Mdocdate: November 25 2014 $
.Dd $Mdocdate: December 8 2014 $
.Dt RAND48 3
.Os
.Sh NAME
@ -22,8 +22,11 @@
.Nm mrand48 ,
.Nm jrand48 ,
.Nm srand48 ,
.Nm srand48_deterministic ,
.Nm seed48 ,
.Nm seed48_deterministic ,
.Nm lcong48
.Nm lcong48_deterministic
.Nd pseudo-random number generators and initialization routines
.Sh SYNOPSIS
.In stdlib.h
@ -41,31 +44,56 @@
.Fn jrand48 "unsigned short xseed[3]"
.Ft void
.Fn srand48 "long seed"
.Ft void
.Fn srand48_deterministic "long seed"
.Ft "unsigned short *"
.Fn seed48 "unsigned short xseed[3]"
.Ft "unsigned short *"
.Fn seed48_deterministic "unsigned short xseed[3]"
.Ft void
.Fn lcong48 "unsigned short p[7]"
.Ft void
.Fn lcong48_deterministic "unsigned short p[7]"
.Sh DESCRIPTION
.Bf -symbolic
This interface is not cryptographically secure, so consider using
.Xr arc4random 3
instead.
Standards insist that this interface return deterministic results.
Unsafe usage is very common, so
.Ox
changed the subsystem to return non-deterministic results by default.
.Ef
.Pp
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 modulus is always fixed at m = 2 ** 48.
r(n) is called the seed of the random number generator.
To satisfy portable code,
.Fn srand48 ,
.Fn seed48 ,
or
.Fn lcong48
should be called to initialize the subsystem.
In
.Ox
the
seeding parameters are ignored, and strong random number results will be
provided from
.Xr arc4random 3.
In other systems, the
parameters prime a simplistic deterministic algorithm.
.Pp
For all the six generator routines described next, the first
computational step is to perform a single iteration of the algorithm.
If the standardized behavior is required then
.Fn srand48_deterministic ,
.Fn seed48_deterministic ,
and
.Fn lcong48_deterministic
can be substituted for
.Fn srand48 ,
.Fn seed48 ,
and
.Fn lcong48 .
That will cause subsequent
calls to
.Fn drand48 ,
.Fn lrand48 ,
and
.Fn jrand48
to return results using the deterministic algorithm.
.Pp
.Fn drand48
and
@ -91,6 +119,21 @@ 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
In the deterministic mode, the
.Fn rand48
family of functions generates 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 modulus 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 ,
.Fn lrand48 ,
and
@ -110,7 +153,7 @@ holds the least significant bits.
.Pp
All functions share the same multiplicand and addend.
.Pp
.Fn srand48
.Fn srand48_deterministic
is used to initialize the internal buffer r(n) of
.Fn drand48 ,
.Fn lrand48 ,
@ -121,7 +164,7 @@ 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
.Fn seed48_deterministic
also initializes the internal buffer r(n) of
.Fn drand48 ,
.Fn lrand48 ,
@ -131,14 +174,14 @@ 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
.Fn seed48_deterministic
returns a pointer to an array of 3 shorts which contains the old seed.
This array is statically allocated, so its contents are lost after
each new call to
.Fn seed48 .
.Fn seed48_deterministic .
.Pp
Finally,
.Fn lcong48
.Fn lcong48_deterministic
allows full control over the multiplicand and addend used in
.Fn drand48 ,
.Fn erand48 ,
@ -169,14 +212,27 @@ The
.Fn drand48 ,
.Fn erand48 ,
.Fn jrand48 ,
.Fn lcong48 ,
.Fn lrand48 ,
.Fn mrand48 ,
.Fn nrand48 ,
.Fn seed48 ,
and
.Fn srand48
.Fn nrand48 ,
functions conform to
.St -p1003.1-2008 .
.Pp
The
.Fn seed48 ,
.Fn srand48 ,
and
.Fn lcong48
function do not conform to
.St -ansiC ,
intentionally.
.Pp
The
.Fn seed48_deterministic ,
.Fn srand48_deterministic ,
and
.Fn lcong48_deterministic
functions are OpenBSD extensions.
.Sh AUTHORS
.An Martin Birgmeier