Re: readir() II

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#3422

From: Pascal J. Bourguignon
Date: Sat, 06 Feb 2010 00:02

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Rainer Weikusat <rweikusat@mssgmbh.com> writes:

> pjb@informatimago.com (Pascal J. Bourguignon) writes:
>
> [...]
>
>> I didn't hide anything.  Some programming language are actually high
>> level programming language, and use normal integer arithmetic, not
>> modulo 2^w arithmetic.
>
> There is no such thing as 'normal integer arithmetic' 

Of course.  Ask anybody in the street how much is 4294967295 + 1.

Arithmetic and integer are things that are defined in mathematic.  When
you use them unqualified, you have an infinite number of integers:

    0 in Integer
    x in Integer => succ(x) in Integer

and the arithmetical operations + and * have the whole Integer set as
image, not just a subset.

> and definitions
> of particular algebraic operations such as +, including the sets they
> operate on, are not structural properties of programming languages.

Of course they are.  

C specifies that its + is actually addition modulo 2^w.

On the other hand, Lisp specifies that its + is the mathematic plus
(restricted to the size of the memory).

(On the other hand, if the syntax of C was defined as:

     int a = b + c [2^(sizeof(int)*CHAR_BIT)];

 instead of:

     int a = b + c;

 a lot less bugs would be written in C.)

-- 
__Pascal Bourguignon__

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From: pjb@informatimago.com (Pascal J. Bourguignon)
Newsgroups: comp.unix.programmer,gnu.gcc.help
Subject: Re: readir() II
Date: Sat, 06 Feb 2010 01:02:42 +0100
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