Re: [PATCH 10/9 v2] test-mergesort: use repeatable random numbers

On Fri, Oct 08 2021, René Scharfe wrote:

Am 08.10.21 um 09:23 schrieb Ævar Arnfjörð Bjarmason:

quoted

Also generally: If you'd like "portable" rand() for a test just shell
out to perl. I ran this on various Perl versions (oldest 5.12) on Debian
Linux, OSX, Solaris & OpenBSD, all returned the same number for both:

    ruby -e 'srand(1); puts rand'; perl -E 'srand(1); say $^V; say rand'

Whereas a C program doing the same:

    #include <stdio.h>
    #include <stdlib.h>

    int main(void)
    {
            srand(1);
            printf("rand = %d\n", rand());
            return 0;
    }

Returns different numbers an all, and on OpenBSD the number is different
each time, per their well-known non-standard srand()/rand() behavior.

For test shell code that needs only a few random numbers this would
be fine.

For test-genrandom it would also work, but I don't see any benefit in
converting it to a scripting language.

Shelling out to a script to avoid a multiplication and a modulo in
test-mergesort is not interesting, to put it mildly.  A mode that sorts
input from stdin like the sort subcommand, but returns the operation
counts, might be useful if you want to test distributions generated by
a Perl script or other data source of your choice.

Yes, it has zero applicablility here.

It was just an aside/FYI since we were on the topic of the
cross-platformness of rand().

I.e. one might assume that for the general problem of seeding something
randomly cross-platform one had to ship a rand(), but usually at least
perl is there ahead of you, and since it has its own rand()...