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				.\"-
				.\" Copyright 2020 Conrad Meyer <cem@FreeBSD.org>. All rights reserved.
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				.\" $FreeBSD$
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				.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 .