freebsd-skq/share/man/man9/prng.9

.\"-
.\" Copyright 2020 Conrad Meyer <cem@FreeBSD.org>.  All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" $FreeBSD$
.\"
.Dd August 5, 2020
.Dt PRNG 9
.Os
.Sh NAME
.Nm prng
.Nd "Kernel pseudo-random number generators"
.Sh SYNOPSIS
.In sys/prng.h
.Ft uint32_t
.Fn prng32 void
.Ft uint32_t
.Fn prng32_bounded "uint32_t bound"
.Ft uint64_t
.Fn prng64 void
.Ft uint64_t
.Fn prng64_bounded "uint64_t bound"
.Sh DESCRIPTION
.Ss GENERIC PRNG ROUTINES
.Nm
is a family of fast,
.Em non-cryptographic
pseudo-random number generators.
Unlike
.Xr random 9 ,
.Fn prng32 ,
.Fn prng32_bounded ,
.Fn prng64 ,
and
.Fn prng64_bounded
avoid shared global state, removing unnecessary contention on SMP
systems.
The routines are not explicitly tied to any specific implementation, and
may produce different specific sequences on different hosts, reboots, or
versions of
.Fx .
Different CPUs in SMP systems are guaranteed to produce different sequences of
integers.
.Pp
For
.Em cryptographically secure
random numbers generated by the
.Xr random 4
kernel cryptographically secure random number generator subsystem, see
.Xr arc4random 9 .
.Pp
.Bl -tag -width indent
.It Fn prng32
Generate a 32-bit integer uniformly distributed in [0, 2^32-1].
.It Fn prng32_bounded bound
Generate an integer uniformly in the range [0, bound-1].
.It Fn prng64
Generate a 64-bit integer uniformly distributed in [0, 2^64-1].
.It Fn prng64_bounded bound
Generate an integer uniformly in the range [0, bound-1].
.El
.Pp
These routines are not reentrant; they are not safe to use in interrupt
handlers ("interrupt filters" in
.Xr bus_setup_intr 9
terminology).
They are safe to use in all other kernel contexts, including interrupt threads
("ithreads").
.Ss REPRODUCIBLE PRNG APIS
In addition to these per-CPU helpers, the
.In sys/prng.h
header also exposes the entire API of the PCG family of PRNGs as inline
functions.
The PCG-C API is described in full at
.Lk https://www.pcg-random.org/using-pcg-c.html .
.Sh HISTORY
.Nm
was introduced in
.Fx 13 .
Add prng(9) API Add prng(9) as a replacement for random(9) in the kernel. There are two major differences from random(9) and random(3): - General prng(9) APIs (prng32(9), etc) do not guarantee an implementation or particular sequence; they should not be used for repeatable simulations. - However, specific named API families are also exposed (for now: PCG), and those are expected to be repeatable (when so-guaranteed by the named algorithm). Some minor differences from random(3) and earlier random(9): - PRNG state for the general prng(9) APIs is per-CPU; this eliminates contention on PRNG state in SMP workloads. Each PCPU generator in an SMP system produces a unique sequence. - Better statistical properties than the Park-Miller ("minstd") PRNG (longer period, uniform distribution in all bits, passes BigCrush/PractRand analysis). - Faster than Park-Miller ("minstd") PRNG -- no division is required to step PCG-family PRNGs. For now, random(9) becomes a thin shim around prng32(). Eventually I would like to mechanically switch consumers over to the explicit API. Reviewed by: kib, markj (previous version both) Discussed with: markm Differential Revision: https://reviews.freebsd.org/D25916 2020-08-13 20:48:14 +00:00			`.\"-`
			`.\" Copyright 2020 Conrad Meyer <cem@FreeBSD.org>. All rights reserved.`
			`.\"`
			`.\" Redistribution and use in source and binary forms, with or without`
			`.\" modification, are permitted provided that the following conditions`
			`.\" are met:`
			`.\" 1. Redistributions of source code must retain the above copyright`
			`.\" notice, this list of conditions and the following disclaimer.`
			`.\" 2. Redistributions in binary form must reproduce the above copyright`
			`.\" notice, this list of conditions and the following disclaimer in the`
			`.\" documentation and/or other materials provided with the distribution.`
			`.\"`
			.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
			`.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE`
			`.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE`
			`.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE`
			`.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL`
			`.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS`
			`.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)`
			`.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT`
			`.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY`
			`.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF`
			`.\" SUCH DAMAGE.`
			`.\"`
			`.\" $FreeBSD$`
			`.\"`
			`.Dd August 5, 2020`
			`.Dt PRNG 9`
			`.Os`
			`.Sh NAME`
			`.Nm prng`
			`.Nd "Kernel pseudo-random number generators"`
			`.Sh SYNOPSIS`
			`.In sys/prng.h`
			`.Ft uint32_t`
			`.Fn prng32 void`
			`.Ft uint32_t`
			`.Fn prng32_bounded "uint32_t bound"`
			`.Ft uint64_t`
			`.Fn prng64 void`
			`.Ft uint64_t`
			`.Fn prng64_bounded "uint64_t bound"`
			`.Sh DESCRIPTION`
			`.Ss GENERIC PRNG ROUTINES`
			`.Nm`
			`is a family of fast,`
			`.Em non-cryptographic`
			`pseudo-random number generators.`
			`Unlike`
			`.Xr random 9 ,`
			`.Fn prng32 ,`
			`.Fn prng32_bounded ,`
			`.Fn prng64 ,`
			`and`
			`.Fn prng64_bounded`
			`avoid shared global state, removing unnecessary contention on SMP`
			`systems.`
			`The routines are not explicitly tied to any specific implementation, and`
			`may produce different specific sequences on different hosts, reboots, or`
			`versions of`
			`.Fx .`
			`Different CPUs in SMP systems are guaranteed to produce different sequences of`
			`integers.`
			`.Pp`
			`For`
			`.Em cryptographically secure`
			`random numbers generated by the`
			`.Xr random 4`
			`kernel cryptographically secure random number generator subsystem, see`
			`.Xr arc4random 9 .`
			`.Pp`
			`.Bl -tag -width indent`
			`.It Fn prng32`
			`Generate a 32-bit integer uniformly distributed in [0, 2^32-1].`
			`.It Fn prng32_bounded bound`
			`Generate an integer uniformly in the range [0, bound-1].`
			`.It Fn prng64`
			`Generate a 64-bit integer uniformly distributed in [0, 2^64-1].`
			`.It Fn prng64_bounded bound`
			`Generate an integer uniformly in the range [0, bound-1].`
			`.El`
			`.Pp`
			`These routines are not reentrant; they are not safe to use in interrupt`
			`handlers ("interrupt filters" in`
			`.Xr bus_setup_intr 9`
			`terminology).`
			`They are safe to use in all other kernel contexts, including interrupt threads`
			`("ithreads").`
			`.Ss REPRODUCIBLE PRNG APIS`
			`In addition to these per-CPU helpers, the`
			`.In sys/prng.h`
			`header also exposes the entire API of the PCG family of PRNGs as inline`
			`functions.`
			`The PCG-C API is described in full at`
			`.Lk https://www.pcg-random.org/using-pcg-c.html .`
			`.Sh HISTORY`
			`.Nm`
			`was introduced in`
			`.Fx 13 .`