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Date: 25 Jun 93 20:50:22 GMT
From: seas.gwu.edu!mfeldman@uunet.uu.net  (Michael Feldman)
Subject: Re: Precedence Rules (was Re: Software vendors not using Ada but C)
Message-ID: <1993Jun25.205022.29499@seas.gwu.edu>
List-Id: <comp.lang.ada>

In article <C96nFu.F4r@ddciiny.UUCP> jls@ddciiny.UUCP (Jonathan Schilling) writ
es:

[stuff deleted]
>
>Probably not.  But people do use mod with types that include negative
>numbers (like INTEGER), and unless the compiler is able to figure out
>that the operands have non-negative values, a fair amount of code will
>be generated for mod.  This is because the semantics for mod do not
>match the semantics of most machines' divide and remainder instructions,
>for negative numbers.
>
>Thus, it is a good habit to only use mod with non-negative subtypes,
>or to avoid mod and use rem (unless you really have negative operands
>and care about the semantics).
>
I agree. This has always been a tough one for me to get across to
students who are used to Pascal's MOD semantics, which of course has
the semantics of Ada's REM. Sigh... Ever try to mechanically translate
some Pascal or Modula-2 code to Ada? Watch out.

Cheers -

Mike Feldman
------------------------------------------------------------------------
Michael B. Feldman -  co-chair, SIGAda Education Committee
Professor, Dept. of Electrical Engineering and Computer Science
The George Washington University -  Washington, DC 20052 USA
202-994-5253 (voice) - 202-994-5296 (fax) - mfeldman@seas.gwu.edu (Internet)
"Pork is what those other guys get from the Government."
------------------------------------------------------------------------