Re: Bit Bashing with Guile

[Maciej Stachowiak <mstachow@mit.edu>]

forcer@mindless.com writes:
> This happens on a 32bit box:
> 
> guile> (logand #b1000000000000000000000000000000 0)
> 0
> guile> (logand #b10000000000000000000000000000000 0)
> ERROR: In procedure logand in expression (logand 2147483648 0):
> ERROR: Wrong type argument in position 1: 2147483648
> ABORT: (wrong-type-arg)
> 
> I conclude from this this that Guile is unable to handle 32+ bit numbers
> with logical functions, is this correct?
> Since i need this (i'm trying to implement CAST-128 encryption as per RFC2144)
> i wonder wether anyone found any solution to this problem already
> short of using vectors for the bit patterns?
> I know i could patch the guile sources to include a CAST encryption function,
> but i'd prefer a Scheme-only solution.
> Any help is appreciated, and thanks in advance,

Guile can logically and anything up to the range of a signed long on
the target platform. IMO, it should use unsigned long instead as a
stopgap; ultimately, the logical boolean functions should be extended
to handle bignums, again IMO. I suspect Jim would accept a patch to
that effect. I would really like such a feature myself (scwm goes
through some gyrations to do bit-twiddling on 32-bit unsigned
quantities) and would code a patch if I had time.

(note: whoever thought of calling the `logical' procedures that? Isn't
`logand' really an arithmetic and, whereas `and' is a logical and? Oh
well...)

 - Maciej