Re: Ada standard and maximum line lengths

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 13-02-01 01:54 , Randy Brukardt wrote:
> "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).

I'm not sure that I understand your conditions on what is "usable", but
the LEB128 encoding (little-endian base 128) used in DWARF works pretty
well for storing unbounded but usually small integers without wasting a
lot of space. An integer is encoded as a sequence of octets, with one
end-marker bit and 7 significand bits in each octet. Numbers from 0 to
127 take one octet, number from 128 to 2**14 - 1 take two octets, and so on.

All records of course become variable-length octet sequences, which
causes processing overhead when storing and loading data. But if the
bottleneck is the disk I/O, that may be tolerable.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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