SPUG: Does Perl Scale? (Was: Evolution of Perl)

Ken McGlothlen mcglk at artlogix.com
Mon Aug 13 19:24:28 CDT 2001

Bill Campbell <bill at celestial.com> writes:

| [...]  I cut the run time from 20 minutes down to under 2 by replacing one
| statement in a subroutine that was executed 20,000 times per run where the
| engineer (I'm a scientist, not a programmer), calculated the square root of
| PI/2 each time the subroutine was called.  [...]  Of course compiler
| technology has progressed a bit since the Bendix Mishawaka (sp?) FORTRAN of
| 1966, but the principle's the same.

Absolutely.  The worst-case scenario I ever ran into was with a program (in C)
that crunched a lot of statistics.  It would take around three days to run with
a 4,000,000 record dataset, and was about 25K lines long.

One day, testing a revision I'd done elsewhere in the code, I started noticing
a curious pattern:  O(n^2).  So I grepped the source code for "sort," out of
curiosity, and discovered the lines:

        int sortdata {
                # look up quicksort and replace when i have time -gb
                [... code for bubblesort ...]

Oh, how I cackled with glee.  :)  Not only could I improve the program, but the
local C library had a qsort routine supplied already.  Some judicious whacking
followed by a single call, and the same 4,000,000 records were being done in
less than half an hour.

They thought I'd broken it.  In fact, *insisted* that I broke it.  Showing them
identical results didn't convince them.  The original programmer, they
insisted, was brilliant, and I couldn't have improved it *that* much (in fact,
he was an awful programmer, and I was constantly fixing issues).  I showed them
the original code, with the comment, but even that wasn't convincing enough.
Eventually, I gave up, and said that I'd restore it, so I did.  Later on, I
talked them into an insertion sort (they understood that), but I just couldn't
get them to go for the quicksort.

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