This adds 3 new variants of the random() function:
random(min integer, max integer) returns integer
random(min bigint, max bigint) returns bigint
random(min numeric, max numeric) returns numeric
Each returns a random number x in the range min <= x <= max.
For the numeric function, the number of digits after the decimal point
is equal to the number of digits that "min" or "max" has after the
decimal point, whichever has more.
The main entry points for these functions are in a new C source file.
The existing random(), random_normal(), and setseed() functions are
moved there too, so that they can all share the same PRNG state, which
is kept private to that file.
Dean Rasheed, reviewed by Jian He, David Zhang, Aleksander Alekseev,
and Tomas Vondra.
Discussion: https://postgr.es/m/CAEZATCV89Vxuq93xQdmc0t-0Y2zeeNQTdsjbmV7dyFBPykbV4Q@mail.gmail.com
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
Dean Rasheed
Bruce Momjian
Tom Lane