Re: [Ocaml-lib-devel] BitSet

[Nicolas C. <war...@fr...>]

>    Hello !
>
>    I made a few changes on the files bitSet.ml and bitSet.mli (see
> attachements). I :
>
> 1 - corrected a few orthograph mistakes (I hope I didn't added new ones)
> 2 - corrected an "lsl" -> "lsr" (the size of a BitSet was 8 times bigger
>      instead of 8 times smaller)
> 3 - suggested the name "copy" which is more usual than "clone"
> 4 - used "blit_string" and "fill_string" for more efficiency
> 5 - added some functions on sets
>
> I hope there are no more mistakes. I have got a question : isn't it
> possible to use the 32 bits of an int (or 64 bits, depending on the
> architecture) for efficients BitSets ? The String functions seem to work
> on 8 bits only.
>
> TIA for your answers,

Thanks, I'll review theses changes.
Concerning the usage of int, OCaml runtime representation is 31 bits. They
are unboxed and shifted by 1 and the lowest bit is set to 1 so it can't be
mistaken with an address since all addresses are always aligned on 2 bytes
(even 4 on most of 32-bits architectures) . So we could use ints as 31 bits
but we would then need to div/mod to get the correct integer. Another nice
thing about strings is that their contents are not scanned by the GC while
Array of ints are.

Regards,
Nicolas Cannasse