Horton

Re: [PATCH] random_normal function

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Paul Ramsey <pramsey@cleverelephant.ca>
Cc: Pgsql Hackers <pgsql-hackers@postgresql.org>
Date: 2022-12-08T22:40:59Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Round off random_normal() test results one more decimal place.

  2. Remove pg_regress' never-documented "ignore" feature.

  3. Upgrade the random.sql regression test.

  4. Invent random_normal() to provide normally-distributed random numbers.

On Thu, Dec 8, 2022 at 2:53 PM Paul Ramsey <pramsey@cleverelephant.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.