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From: Adam Beneschan <adam@irvine.com>
Newsgroups: comp.lang.ada
Subject: Re: Reading and writing a big file in Ada (GNAT) on Windows XP
Date: 3 May 2007 13:27:28 -0700
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Date: 2007-05-03T13:27:28-07:00
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On May 2, 11:31 pm, Fionn Mac Cumhaill <invisi...@hiding.from.spam>
wrote:

> I did do further investigation; I made a copy of the now-working
> program and threw most of the program away, leaving only a very simple
> program which read the large input file, but made no changes and did
> no output. I added code to track the run time and put the buffer clear
> back in. It read the 10 million lines in just a little over five
> minutes. I then put  Index back and used it to search the buffer for a
> short string that would never be found, seatching forwards from the
> beginning of the input buffer. Bingo. Run time increased to a bit more
> than 1-1/2 hours.

It strikes me that Index is the kind of function that really ought to
be written in assembly language, at least partially.  I notice that
the version of Linux that I'm using has a built-in function to search
memory for a substring; this is very descriptively called memmem() and
has the amusing profile

   void *memmem (const void *needle, size_t needlelen,
                            const void *haystack, size_t haystacklen);

according to the man page.  But I assume this is written to use
registers optimally and take advantage of the REP instructions (on an
x86 or Pentium).  I don't know how GNAT implements Index---I haven't
looked into it.

                                    -- Adam