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Replace random(), pg_erand48(), etc with a better PRNG API and algorithm.

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Standardize on xoroshiro128** as our basic PRNG algorithm, eliminating
a bunch of platform dependencies as well as fundamentally-obsolete PRNG
code.  In addition, this API replacement will ease replacing the
algorithm again in future, should that become necessary.

xoroshiro128** is a few percent slower than the drand48 family,
but it can produce full-width 64-bit random values not only 48-bit,
and it should be much more trustworthy.  It's likely to be noticeably
faster than the platform's random(), depending on which platform you
are thinking about; and we can have non-global state vectors easily,
unlike with random().  It is not cryptographically strong, but neither
are the functions it replaces.

Fabien Coelho, reviewed by Dean Rasheed, Aleksander Alekseev, and myself

Discussion: https://postgr.es/m/alpine.DEB.2.22.394.2105241211230.165418@pseudo
This commit is contained in:
Tom Lane
2021-11-28 21:32:36 -05:00
parent f44ceb46ec
commit 3804539e48
50 changed files with 543 additions and 480 deletions
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5
contrib/tablefunc/tablefunc.c
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@ -36,6 +36,7 @@
#include "access/htup_details.h"
#include "catalog/pg_type.h"
#include "common/pg_prng.h"
#include "executor/spi.h"
#include "funcapi.h"
#include "lib/stringinfo.h"
@ -290,8 +291,8 @@ get_normal_pair(float8 *x1, float8 *x2)
do
{
u1 = (float8) random() / (float8) MAX_RANDOM_VALUE;
u2 = (float8) random() / (float8) MAX_RANDOM_VALUE;
u1 = pg_prng_double(&pg_global_prng_state);
u2 = pg_prng_double(&pg_global_prng_state);
v1 = (2.0 * u1) - 1.0;
v2 = (2.0 * u2) - 1.0;