Re: [PATCH] random_normal function

On Thu, Dec 8, 2022 at 2:53 PM Paul Ramsey <pramsey(at)cleverelephant(dot)ca>
wrote:

>
> random_normal(stddev float8 DEFAULT 1.0, mean float8 DEFAULT 0.0)
>

Any particular justification for placing stddev before mean? A brief
survey seems to indicate other libraries, as well as (at least for me)
learned convention, has the mean be supplied first, then the standard
deviation. The implementation/commentary seems to use that convention as
well.

Some suggestions:

/* Apply optional user parameters */ - that isn't important or even what is
happening though, and the body of the function shouldn't care about the
source of the values for the variables it uses.

Instead:
/* Transform the normal standard variable (z) using the target normal
distribution parameters */

Personally I'd probably make that even more explicit:

+ float8 z
...
* z = pg_prng_double_normal(&drandom_seed)
+ /* ... */
* result = (stddev * z) + mean

And a possible micro-optimization...

+ bool rescale = true
+ if (PG_NARGS() = 0)
+ rescale = false
...
+ if (rescale)
... result = (stddev * z) + mean
+ else
+ result = z

David J.