Re: Strings Fixed, Bounded, and Counted. Performance Inquiry.

[Freejack <user@nospam.net>]

On Mon, 27 Oct 2003 12:18:48 -0500, Stephen Leake wrote:

 
>> A bit more flexible than Fixed strings,
> 
> How?

It was my understanding(I could be wrong here) that a Fixed string is
unmodifiable without access to functions provided in the package. A
Counted string is modifiable outside the package provided functions and
procedures. No?

 
>> a heck of a lot faster than Null terminated strings.
> 
> Depends on what you are doing. Copying the strings character by
> character is the same speed for either construct. Block copy is faster
> with a count on most machines. But most algorithms for processing
> strings operate character by character, so it doesn't really matter.
> 
> Safety is another issue; with a count (or bounds) it is possible to
> check array indices before fetching or storing.

 So essentially, with a Fixed string, I can have the compiler generate
machine code to grab a block of length X, and shove it into an empty
block of length Y if Y > X? All on one I/O procedure? (Thinking of the
Linux "sendfile()" and "iovec()" functions here.)
I really want to avoid character by character transfer when it's not
necessary.
Also, if I can read the first element, and see that the string has twenty
characters, I can have the program inline a procedure x/20 times, rather
than using a Counter and loop structure. 
 
>> I'm gonna write my own experimental package if nobody else has
> 
> Be sure you define _precisely_ what you want the package to do, and see
> if Ada already has it, before you spend time implementing it.
 
I am definitely being specific in my package spec. You're right. Aside
from a couple quirks of my own design, bounded strings do the right
thing. As do Fixed Strings.

I'll keep playing with 'em and tell you what I come up with. Heh.

Thanks.

Freejack