Re: New Book: The School of Niklaus Wirth

> >A subrange is a thing, the kind of animal containing the value is
> >another.


VBDis


> IMO subranges with explicit bounds are the most portable kind of
> data types. The lower bound indicates whether the value is signed
> or unsigned, and the compiler can choose the best fitting data type
> for the requested precision.


Now you have to decide what to do with an expression like (-i)
for a "subrange" like 0..100. To convert to a larger range,
to wrap or to detect a range error ?...


There a distinction between types and subtypes, "universal integers"
or integers with a certain bitwise description is important.


> Delphi internally describes all integral data types by subranges,
> including the predefined data types.


Its predecesor (Turbo Pascal) had such a description in its System
unit. But there was a total mess due to this minimalist design. You
could (or had to) do "unsigned" 32-bit operations (shift xor etc.)
with a signed type (longint) and the automatic conversions between
internal representations added a lot of extra machine code. Add to it
that there was absolutely no code optimisation... Maybe it has been
redesigned in some version of Delphi - has it ?


_____________________________________________
Gautier -- http://members.nbci.com/gdemont/

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