Re: Ada standard and maximum line lengths

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wccwquucd1x.fsf@shell01.TheWorld.com...
...
>>...but I still
>> wouldn't like wasting significant amounts of memory (line/position
>> information being stored in almost every symbol table entry) to carry 
>> almost
>> no information.
>
> There are various ways to store line/column numbers compactly without
> limiting line lengths.

Really? Do tell! I know of no such technique that still would be usable 
(meaning does not involve indirection, which would add complication and 
fragmentation issues, and can be used at any time without calculation, 
because you don't know ahead of time when and where you'll need to generate 
error messages, debugging information, and traces). If you're not willing to 
waste space, you have to limit the size to 24-bits (maybe 32-bits at the 
outside); you might be able to use a couple of bits to control the divide 
between line numbers and positions, but really long line at the end of a 
really long file couldn't be handled (you'd run out of bits). For 24-bits, 
it's not worth it, and even using 32 you might as well just use a 10-bit 
position number and be done with it. If you only needed relative encoding, 
you could store the change from the last item in each time (limited to a 
small number of bits); that might work in the token stream [not the way we 
use it, but that's a different issue], but it wouldn't work in the symbol 
table or debugging information.

Janus/Ada has line number and line position types declared in the Host 
package; these can be adjusted of course but we do the Ada thing and use 
strong typing so that someone doesn't use a line number as if it is a type 
handle. [Someone, ahem, has done that in the past.] So the storage options 
are limited.

                                                     Randy.