Re: [BLACKBOX] CONSTant expressions

From: Campbell, Robert (SELEX GALILEO, UK) <"Campbell,>
Date: Thu, 31 Jan 2008 09:06:53 -0000

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Content-type: text/plain

Hello

I implied earlier that CONST multiplies had some problems.
Below is a clearer example:

MODULE DemoConstMult;IMPORT StdLog;

(*
PROCEDURE NotUsed;
  CONST
    zero = 0.;
  VAR
    z : REAL;
  BEGIN
    z := zero
  END NotUsed;
*)

PROCEDURE Do*;
  CONST
    aa = -5.;
    zz = aa * 0.;
  VAR
    zero, inf : REAL;
  BEGIN
    zero := zz;
    inf := 1. / zero;

    StdLog.String ('inf = '); StdLog.Real (inf); StdLog.Ln
  END Do;

END DemoConstMult.

<Q> DevDebug.Unload
<Q> DemoConstMult.Do

 
This module outputs "inf = -inf", as it should.
But if I uncomment NotUsed it outputs "inf = inf".

I have a theory (well a guess actually!).

The compiler puts the CONSTants it needs into a table.
It avoids duplicates by not repeating the same constant more than once.
It uses '=' as a test for 'sameness'.
This is wrong. (+0.) = (-0.), but they are not the same.


I think I regard this behaviour as a compiler bug.


Regards,

Robert

SELEX Sensors and Airborne Systems Limited
Registered Office: Sigma House, Christopher Martin Road, Basildon, Essex SS14 3EL
A company registered in England & Wales. Company no. 02426132
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Received on Thu Jan 31 2008 - 10:06:53 UTC