**diff options**

author | Conrad Meyer <cem@FreeBSD.org> | 2020-08-13 20:48:14 +0000 |
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committer | Conrad Meyer <cem@FreeBSD.org> | 2020-08-13 20:48:14 +0000 |

commit | 8a0edc914ffdda876987add5128da3ee236a6a12 (patch) | |

tree | 1555e019838dfb5459fdcfad310285ab48d7f879 /sys/libkern | |

parent | 1e04d9ff3e2565a402e449eb59b30b826bb2894a (diff) | |

download | src-8a0edc914ffdda876987add5128da3ee236a6a12.tar.gz src-8a0edc914ffdda876987add5128da3ee236a6a12.zip |

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

Notes

Notes:
svn path=/head/; revision=364219

Diffstat (limited to 'sys/libkern')

-rw-r--r-- | sys/libkern/random.c | 35 |

1 files changed, 3 insertions, 32 deletions

diff --git a/sys/libkern/random.c b/sys/libkern/random.c index e5e9de6108e1..23a8887fa49b 100644 --- a/sys/libkern/random.c +++ b/sys/libkern/random.c @@ -36,43 +36,14 @@ __FBSDID("$FreeBSD$"); #include <sys/types.h> #include <sys/libkern.h> +#include <sys/prng.h> #include <sys/systm.h> -static u_long randseed = 937186357; /* after srandom(1), NSHUFF counted */ - /* - * Pseudo-random number generator for perturbing the profiling clock, - * and whatever else we might use it for. The result is uniform on - * [0, 2^31 - 1]. + * Pseudo-random number generator. The result is uniform in [0, 2^31 - 1]. */ u_long random(void) { - static bool warned = false; - - long x, hi, lo, t; - - /* Warn only once, or it gets very spammy. */ - if (!warned) { - gone_in(13, - "random(9) is the obsolete Park-Miller LCG from 1988"); - warned = true; - } - - /* - * Compute x[n + 1] = (7^5 * x[n]) mod (2^31 - 1). - * From "Random number generators: good ones are hard to find", - * Park and Miller, Communications of the ACM, vol. 31, no. 10, - * October 1988, p. 1195. - */ - /* Can't be initialized with 0, so use another value. */ - if ((x = randseed) == 0) - x = 123459876; - hi = x / 127773; - lo = x % 127773; - t = 16807 * lo - 2836 * hi; - if (t < 0) - t += 0x7fffffff; - randseed = t; - return (t); + return (prng32()); } |