🚀 go-pugleaf

jguthrie@brokersys.com wrote:
>Michel De Rosa (aliath@nyongwa.montreal.qc.ca) wrote:

>: Bit operations.. unfortunately with pre-ISO compilers, we where usually
>: stuck with multiplying or dividing by 2, for shift operations (rotate is
>: a tad more involved), now ISO also provides functions for those.. for
>: and/or/xor etc.. it's always been possible to do these, using the set
>: operators.. first coerce to a BITSET...

>Please don't talk down to me.  I know how to manipulate bitsets, but 
>do WHAT to a BITSET?   As far as I know, NONE of the M2 compilers I have
>ever used allow me to convert between any kind of number and any kind of
>set.  Otherwise, I'd have used that rather than mucking about with assembly
>language.  

>I know that that isn't mentioned anywhere in PIM3C.

Yes it is.  Let c be a CARDINAL (for example) and let b be a BITSET.
Then in ISO M2 you can write  b := CAST(BITSET, c).  In the PIM3
version of M2 the syntax is more obscure:  b := BITSET(c).
The second form should be supported by any M2 compiler you can
lay your hands on.

A trick used by some programmers is to abuse the concept of
a record with variants:

     TYPE Cheat = RECORD
                      CASE :BOOLEAN OF
                          | FALSE: bits: BITSET;
                          | TRUE:  val: CARDINAL;
                      END (*CASE*)
                  END (*RECORD*)

Now, with x a variable of type Cheat, you can do bit operations
on x.bits, and the answer will turn up in x.val.  This isn't
portable, but then operations requiring type-casting are
inherently non-portable in any language.

--
Peter Moylan                       peter@ee.newcastle.edu.au
                           ftp://ee.newcastle.edu.au/pub/www/Moylan.html