🚀 go-pugleaf

jguthrie@brokersys.com wrote:
: Eric Obermuhlner (erico@cnmat.berkeley.edu) wrote:
: : Hi out there
: 
: : How do I do the ugly things that C programmers like so very much in Modula 2?
: : Like getting a pointer to a var, pointer arithmetic, bit operations (shift, and, or, exor).
: 
: Well, I wound up doing that kind of stuff in assembly language.  I also
: concluded that the insistence on abstraction above all else was sometimes 
: detrimental to my efforts to easily write things such as CRC routines.
: 
Well there are a few reasons why we consider this sort of thing 'ugly'..
Even so, there should be little need to go to asm for them..

Assigning a pointer to an ordinal variable, would be done thru type
coercion, as in:   ordVar := CARDINAL(ptrVar);

THis assumes, of course, that the length (bit-size) of a CARDINAL is the
same as for a pointer..

Pointer arith.. ugh!!! well if you *must*, coercing the pointer to a
cardinal will often do the trick... but if you work on a platform with
segmented addresses you'll have a lot of fun.. ISO helps, here by providing
functions for incrementing and decrementing Adresses..

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, then apply these ops:

  +  ... set union,   'or'
  *  ... set intersection,  'and'
  /  ... set symmetric difference,  'xor'
  -  ... set difference,  'and not'

Further you can more easily test for a bit, using:   bit IN someBitset

Set a specific bit:  INCL(someBitset, bitToSet)
Reset a specific bit:  EXCL(someBitset, bitToReset)

Ciao!
Michel De Rosa
Aliath@nyongwa.montreal.qc.ca