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
This commit is contained in:
Conrad Meyer
parent
1e04d9ff3e
commit
8a0edc914f
@ -272,6 +272,7 @@ MAN= accept_filter.9 \
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printf.9 \
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prison_check.9 \
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priv.9 \
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prng.9 \
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proc_rwmem.9 \
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pseudofs.9 \
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psignal.9 \
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@ -1745,6 +1746,10 @@ MLINKS+=printf.9 log.9 \
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printf.9 uprintf.9
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MLINKS+=priv.9 priv_check.9 \
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priv.9 priv_check_cred.9
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MLINKS+=prng.9 prng32.9 \
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prng.9 prng32_bounded.9 \
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prng.9 prng64.9 \
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prng.9 prng64_bounded.9
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MLINKS+=proc_rwmem.9 proc_readmem.9 \
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proc_rwmem.9 proc_writemem.9
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MLINKS+=psignal.9 gsignal.9 \
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99
share/man/man9/prng.9
Normal file
99
share/man/man9/prng.9
Normal file
@ -0,0 +1,99 @@
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.\"-
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.\" Copyright 2020 Conrad Meyer <cem@FreeBSD.org>. All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd August 5, 2020
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.Dt PRNG 9
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.Os
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.Sh NAME
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.Nm prng
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.Nd "Kernel pseudo-random number generators"
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.Sh SYNOPSIS
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.In sys/prng.h
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.Ft uint32_t
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.Fn prng32 void
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.Ft uint32_t
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.Fn prng32_bounded "uint32_t bound"
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.Ft uint64_t
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.Fn prng64 void
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.Ft uint64_t
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.Fn prng64_bounded "uint64_t bound"
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.Sh DESCRIPTION
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.Ss GENERIC PRNG ROUTINES
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.Nm
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is a family of fast,
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.Em non-cryptographic
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pseudo-random number generators.
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Unlike
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.Xr random 9 ,
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.Fn prng32 ,
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.Fn prng32_bounded ,
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.Fn prng64 ,
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and
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.Fn prng64_bounded
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avoid shared global state, removing unnecessary contention on SMP
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systems.
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The routines are not explicitly tied to any specific implementation, and
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may produce different specific sequences on different hosts, reboots, or
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versions of
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.Fx .
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Different CPUs in SMP systems are guaranteed to produce different sequences of
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integers.
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.Pp
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For
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.Em cryptographically secure
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random numbers generated by the
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.Xr random 4
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kernel cryptographically secure random number generator subsystem, see
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.Xr arc4random 9 .
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.Pp
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.Bl -tag -width indent
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.It Fn prng32
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Generate a 32-bit integer uniformly distributed in [0, 2^32-1].
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.It Fn prng32_bounded bound
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Generate an integer uniformly in the range [0, bound-1].
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.It Fn prng64
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Generate a 64-bit integer uniformly distributed in [0, 2^64-1].
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.It Fn prng64_bounded bound
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Generate an integer uniformly in the range [0, bound-1].
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.El
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.Pp
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These routines are not reentrant; they are not safe to use in interrupt
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handlers ("interrupt filters" in
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.Xr bus_setup_intr 9
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terminology).
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They are safe to use in all other kernel contexts, including interrupt threads
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("ithreads").
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.Ss REPRODUCIBLE PRNG APIS
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In addition to these per-CPU helpers, the
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.In sys/prng.h
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header also exposes the entire API of the PCG family of PRNGs as inline
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functions.
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The PCG-C API is described in full at
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.Lk https://www.pcg-random.org/using-pcg-c.html .
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.Sh HISTORY
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.Nm
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was introduced in
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.Fx 13 .
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@ -3834,6 +3834,7 @@ kern/subr_pctrie.c standard
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kern/subr_pidctrl.c standard
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kern/subr_power.c standard
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kern/subr_prf.c standard
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kern/subr_prng.c standard
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kern/subr_prof.c standard
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kern/subr_rangeset.c standard
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kern/subr_rman.c standard
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@ -36,22 +36,16 @@
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#ifndef PCG_VARIANTS_H_INCLUDED
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#define PCG_VARIANTS_H_INCLUDED 1
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#include <inttypes.h>
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#if __SIZEOF_INT128__
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#if defined(__SIZEOF_INT128__) && __SIZEOF_INT128__
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typedef __uint128_t pcg128_t;
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#define PCG_128BIT_CONSTANT(high,low) \
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((((pcg128_t)high) << 64) + low)
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#define PCG_HAS_128BIT_OPS 1
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#else
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#define PCG_HAS_128BIT_OPS 0
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#endif
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#if __GNUC_GNU_INLINE__ && !defined(__cplusplus)
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#error Nonstandard GNU inlining semantics. Compile with -std=c99 or better.
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/* We could instead use macros PCG_INLINE and PCG_EXTERN_INLINE
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but better to just reject ancient C code. */
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#endif
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#if __cplusplus
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#ifdef __cplusplus
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extern "C" {
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#endif
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@ -65,8 +59,8 @@ inline uint8_t pcg_rotr_8(uint8_t value, unsigned int rot)
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* recognizing idiomatic rotate code, so for clang we actually provide
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* assembler directives (enabled with PCG_USE_INLINE_ASM). Boo, hiss.
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*/
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#if PCG_USE_INLINE_ASM && __clang__ && (__x86_64__ || __i386__)
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asm ("rorb %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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#if PCG_USE_INLINE_ASM && defined(__clang__) && (defined(__x86_64__) || defined(__i386__))
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__asm__ ("rorb %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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#else
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return (value >> rot) | (value << ((- rot) & 7));
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@ -75,8 +69,8 @@ inline uint8_t pcg_rotr_8(uint8_t value, unsigned int rot)
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inline uint16_t pcg_rotr_16(uint16_t value, unsigned int rot)
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{
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#if PCG_USE_INLINE_ASM && __clang__ && (__x86_64__ || __i386__)
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asm ("rorw %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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#if PCG_USE_INLINE_ASM && defined(__clang__) && (defined(__x86_64__) || defined(__i386__))
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__asm__ ("rorw %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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#else
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return (value >> rot) | (value << ((- rot) & 15));
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@ -85,8 +79,8 @@ inline uint16_t pcg_rotr_16(uint16_t value, unsigned int rot)
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inline uint32_t pcg_rotr_32(uint32_t value, unsigned int rot)
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{
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#if PCG_USE_INLINE_ASM && __clang__ && (__x86_64__ || __i386__)
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asm ("rorl %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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#if PCG_USE_INLINE_ASM && defined(__clang__) && (defined(__x86_64__) || defined(__i386__))
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__asm__ ("rorl %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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#else
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return (value >> rot) | (value << ((- rot) & 31));
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@ -95,10 +89,10 @@ inline uint32_t pcg_rotr_32(uint32_t value, unsigned int rot)
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inline uint64_t pcg_rotr_64(uint64_t value, unsigned int rot)
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{
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#if 0 && PCG_USE_INLINE_ASM && __clang__ && __x86_64__
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#if 0 && PCG_USE_INLINE_ASM && defined(__clang__) && (defined(__x86_64__) || defined(__i386__))
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/* For whatever reason, clang actually *does* generate rotq by
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itself, so we don't need this code. */
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asm ("rorq %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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__asm__ ("rorq %%cl, %0" : "=r" (value) : "0" (value), "c" (rot));
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return value;
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#else
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return (value >> rot) | (value << ((- rot) & 63));
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@ -2491,18 +2485,6 @@ typedef struct pcg_state_setseq_128 pcg128i_random_t;
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#define pcg128i_advance_r pcg_setseq_128_advance_r
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#endif
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extern uint32_t pcg32_random(void);
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extern uint32_t pcg32_boundedrand(uint32_t bound);
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extern void pcg32_srandom(uint64_t seed, uint64_t seq);
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extern void pcg32_advance(uint64_t delta);
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#if PCG_HAS_128BIT_OPS
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extern uint64_t pcg64_random(void);
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extern uint64_t pcg64_boundedrand(uint64_t bound);
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extern void pcg64_srandom(pcg128_t seed, pcg128_t seq);
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extern void pcg64_advance(pcg128_t delta);
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#endif
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/*
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* Static initialization constants (if you can't call srandom for some
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* bizarre reason).
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@ -2536,7 +2518,7 @@ extern void pcg64_advance(pcg128_t delta);
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#define PCG128I_INITIALIZER PCG_STATE_SETSEQ_128_INITIALIZER
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#endif
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#if __cplusplus
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#ifdef __cplusplus
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}
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#endif
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131
sys/kern/subr_prng.c
Normal file
131
sys/kern/subr_prng.c
Normal file
@ -0,0 +1,131 @@
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/*-
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* SPDX-License-Identifier: BSD-2-Clause-FreeBSD
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*
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* Copyright 2020 Conrad Meyer <cem@FreeBSD.org>. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*/
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#include <sys/cdefs.h>
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__FBSDID("$FreeBSD$");
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#include <sys/param.h>
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#include <sys/kernel.h>
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#include <sys/pcpu.h>
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#include <sys/prng.h>
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#include <sys/smp.h>
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#include <sys/systm.h>
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#if !PCG_HAS_128BIT_OPS
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/* On 32-bit platforms, gang together two 32-bit generators. */
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typedef struct {
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pcg32u_random_t states[2];
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} pcg64u_random_t;
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static inline void
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pcg64u_srandom_r(pcg64u_random_t *state64, uint64_t seed)
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{
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pcg32u_srandom_r(&state64->states[0], seed);
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pcg32u_srandom_r(&state64->states[1], seed);
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}
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static inline uint64_t
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pcg64u_random_r(pcg64u_random_t *state64)
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{
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return ((((uint64_t)pcg32u_random_r(&state64->states[0])) << 32) |
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pcg32u_random_r(&state64->states[1]));
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}
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static inline uint64_t
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pcg64u_boundedrand_r(pcg64u_random_t *state64, uint64_t bound)
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{
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uint64_t threshold = -bound % bound;
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for (;;) {
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uint64_t r = pcg64u_random_r(state64);
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if (r >= threshold)
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return (r % bound);
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}
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}
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#endif
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DPCPU_DEFINE_STATIC(pcg32u_random_t, pcpu_prng32_state);
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DPCPU_DEFINE_STATIC(pcg64u_random_t, pcpu_prng64_state);
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static void
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prng_init(void *dummy __unused)
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{
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pcg32u_random_t *state;
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pcg64u_random_t *state64;
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int i;
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CPU_FOREACH(i) {
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state = DPCPU_ID_PTR(i, pcpu_prng32_state);
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pcg32u_srandom_r(state, 1);
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state64 = DPCPU_ID_PTR(i, pcpu_prng64_state);
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pcg64u_srandom_r(state64, 1);
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}
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}
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SYSINIT(prng_init, SI_SUB_CPU, SI_ORDER_ANY, prng_init, NULL);
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uint32_t
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prng32(void)
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{
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uint32_t r;
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critical_enter();
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r = pcg32u_random_r(DPCPU_PTR(pcpu_prng32_state));
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critical_exit();
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return (r);
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}
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uint32_t
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prng32_bounded(uint32_t bound)
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{
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uint32_t r;
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critical_enter();
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r = pcg32u_boundedrand_r(DPCPU_PTR(pcpu_prng32_state), bound);
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critical_exit();
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return (r);
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}
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uint64_t
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prng64(void)
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{
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uint64_t r;
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critical_enter();
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r = pcg64u_random_r(DPCPU_PTR(pcpu_prng64_state));
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critical_exit();
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return (r);
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}
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uint64_t
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prng64_bounded(uint64_t bound)
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{
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uint64_t r;
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critical_enter();
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r = pcg64u_boundedrand_r(DPCPU_PTR(pcpu_prng64_state), bound);
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critical_exit();
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return (r);
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}
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@ -36,43 +36,14 @@ __FBSDID("$FreeBSD$");
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#include <sys/types.h>
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#include <sys/libkern.h>
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#include <sys/prng.h>
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#include <sys/systm.h>
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static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */
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/*
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* Pseudo-random number generator for perturbing the profiling clock,
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* and whatever else we might use it for. The result is uniform on
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* [0, 2^31 - 1].
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* Pseudo-random number generator. The result is uniform in [0, 2^31 - 1].
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*/
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u_long
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random(void)
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{
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static bool warned = false;
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long x, hi, lo, t;
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/* Warn only once, or it gets very spammy. */
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if (!warned) {
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gone_in(13,
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"random(9) is the obsolete Park-Miller LCG from 1988");
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warned = true;
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}
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/*
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* Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1).
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* From "Random number generators: good ones are hard to find",
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* Park and Miller, Communications of the ACM, vol. 31, no. 10,
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* October 1988, p. 1195.
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*/
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/* Can't be initialized with 0, so use another value. */
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if ((x = randseed) == 0)
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x = 123459876;
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hi = x / 127773;
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lo = x % 127773;
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t = 16807 * lo - 2836 * hi;
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if (t < 0)
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t += 0x7fffffff;
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randseed = t;
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return (t);
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return (prng32());
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}
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20
sys/sys/prng.h
Normal file
20
sys/sys/prng.h
Normal file
@ -0,0 +1,20 @@
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/*-
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* This file is in the public domain.
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*
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* $FreeBSD$
|
||||
*/
|
||||
|
||||
#ifndef _SYS_PRNG_H_
|
||||
#define _SYS_PRNG_H_
|
||||
|
||||
#define PCG_USE_INLINE_ASM 1
|
||||
#include <contrib/pcg-c/include/pcg_variants.h>
|
||||
|
||||
#ifdef _KERNEL
|
||||
__uint32_t prng32(void);
|
||||
__uint32_t prng32_bounded(__uint32_t bound);
|
||||
__uint64_t prng64(void);
|
||||
__uint64_t prng64_bounded(__uint64_t bound);
|
||||
#endif
|
||||
|
||||
#endif
|
||||
Loading…
Reference in New Issue
Block a user