Re: Help with type conversion needed

[njb@res.eng.uiowa.edu (Nate Bohlmann)]

Robert Dewar (dewar@cs.nyu.edu) wrote:
: Nathan keeps worrying about some bias that needs to be added when
: converting unsigned values to signed and vice versa. The whole point
: of 2's complement notation is that no such bias is required.

: For example 16#FFFF# is either -1 or 65_535 depending on how you
: interprete it (signed or unsigned).

Right, and this is why I don't want it to be a noop.  If I have a range
of values from -32768 to 32767, and I want to shift that range to 0 to
65535, simply doing a noop is NOT sufficient..  i.e. -32768 maps to 0 
and 32767 maps to 65535.  -1 should map to 32767, NOT 65535.   

If I simply interpret the bit pattern as signed or unsigned I will not
keep the relative values that I need.. 

I guess this isn't really a type conversion question so much as a range
conversion question.  I fooled the 2.07 GNAT complier by adding 32767 and 1
and the compiler spit out the proper add but the 3.01 compiler complains
that the addition is out of range (as I think it probably should).

As far as a real example, I'm not quite sure I could give one other than
what I've said above.  It would just be a simple addition that fails in
the semantic checker because what I'm trying to add is out of range.

I think probably the best answer so far is to use a bigger (in terms of
bits).  Is this just a nasty side effect of the strong typing? (btw, I'm
a very strong supporter of the strong typing paradigm lest any of you
get the wrong idea.. :-)  I just would like to be able to do this eloquently
and can't seem to find a way to do it.

Nate

--
Nathan Bohlmann                           preferred->   njb@res.eng.uiowa.edu
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