Re: Integers on 64-bit machines

Hans-Peter Diettrich wrote:


> [Defining the range for each variable is one of those ideas that seems
> like a good idea but in practice, programmers don't do it. In Multics
> PL/I programs, all the variables were FIXED BIN(35) because everyone
> knew that was how you got a word variable. On IBM mainframes, they
> were all FIXED BIN(31). -John]


Perhaps somebody can help me with a proper citation: AFAIR Bjarne
Stroustrup (or Wirth?) said about OOP, that it makes a difference
whether a langaage *supports* OOP, or whether it *encourages* to use OOP.


The same for other features of a language. In strictly typed languages,
like Delphi/OPL, it's common practice to use subrange types, along with
enumerated and set types.


Subrange and other types can not only simplify the design and debugging
of a program, they also can lead to faster execution, due to better
optimization criteria for the compiler.


Consider a common situation: the difference between two n-bit values
requires n+1 bits, or overflows can occur when less bits are used for
the result. Using an subrange type of wordsize-n bits, both the user and
the compiler can be sure that a sum or difference cannot produce an
overflow, in computations with full wordsize registers or variables.


A common situation, found in many open source C codes, are comparisons
of signed and unsigned values. The Delphi compiler warns the user, that
the comparison requires to extend the values to the next higher type. I
dunno what a C compiler will do in such cases, but in Delphi I can use
appropriate subrange types to eliminate such conversions.


Now tell me please, how one can prevent overflows or inappropriate or
bloated comparison code, when e.g. only a single integer type is available.


DoDi

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