Re: Internal Representation of Strings

"Bartc" <bartc@freeuk.com> wrote in message news:09-02-084@comp.compilers...


> I'm thinking of the following representation for short strings 2 to 256
> characters, designed for use as array and record elements.


> So I store the length using the final two bytes as follows, for a string
> with 8 bytes:
>
> 0,0 Length is 0
> 0,N Length is N (up to 6)
> X,0 Length is 7
> X,Y Length is 8


> [This sounds awfully complicated for an in-memory design. Why not just
> use a four byte length and code more compactly if needed on I/O. -John]


I use a 4-byte length in other places, but where a string is short, it
does seem attractive to use all available bytes and not waste one for
a length or terminator (and if I wanted up to 8 useable characters,
that would mean using an odd 9-byte field).


Extracting the length is perhaps 3 x86 instructions for most strings,
maximum 5. Compared with one instruction to pick up the length from a
regular string. (Of course I haven't actually tried it yet..)


--
Bartc
[In a world where laptops have a gigabyte of RAM, what's the point in trying to save
a few bytes with structures in memory? -John]

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