Re: CRC in Ada?

[fjh@mundook.cs.mu.OZ.AU (Fergus Henderson)]

kilgallen@eisner.decus.org (Larry Kilgallen) writes:

>bobduff@world.std.com (Robert A Duff) writes:
>> 
>> I think I disagree.  Buffering should be the job of the OS and/or
>> standard libraries.  Not every program.
>
>While theoretical computing and Alan Turing may be centered on
>the equivalence and correctness of programs, in the real world
>performance is also a consideration.

Sure.  That's why buffering is needed.  But buffering  should be the
job of the OS and/or standard libraries.

>Just as those using intense
>computation will be concerned about the efficiency of their
>algorithms, those accessing large databases will take care
>regarding order-of-access so as not to go skipping over the
>whole thing when some locality-of-reference would yield better
>performance. 

Sure.  No disagreement here.

>Those reading sequentially from disk should
>likewise concern themselves with performance, and 512 calls
>to even the lightest-weight library is too much if a single
>call would do.

Nonsense, if the calls are inlined, and the compiler does a good
job of optimization, there is no reason why the cost need be too much.

>For the stated problem (CRC) reading large
>blocks is a clear win.

Yes, but that is true for just about all performance-intensive stream
I/O tasks.  That's why it makes sense for this to be done by the
standard library and/or OS.

>> I'm not sure why reading a file character-by-character is "C-like".
>> It seems like the natural way to write lots of programs, in any
>> language.  The underlying language and OS should ensure that it can be
>> done efficiently (by making the "give-me-a-char" routine read from a
>> buffer whenever appropriate).
>
>In my experience it is generally C programmers who make this mistake.

Why is it a mistake?

If the implementation implements it efficiently, as it should,
I don't see any reason to regard using such a mechanism as a mistake.

--
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: <http://www.cs.mu.oz.au/~fjh>   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.