RE: Numeric problem in BlackBox 1.4

From: [at]} <support{>
Date: Mon, 17 Feb 2003 18:29:13 +0100

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Content-type: text/plain

Wojtek,

The exact value of 1.000000000000000001 can't be stored in a variable of
type REAL. That's why the compiler truncates this number to r = 1.0 in the
assignment r := 1.000000000000000001. You can check this in the debugger by
inserting a HALT statement after the assignment.

Best regards,
Marc
Oberon microsystems, Inc.


> -----Original Message-----
> From: Wojtek Skulski [mailto:skulski{([at]})nowhere.xy
> Sent: Sonntag, 16. Februar 2003 04:52
> To: support{([at]})nowhere.xy
> Cc: Wojtek Skulski; BlackBox
> Subject: Numeric problem in BlackBox 1.4
>
>
> Hello:
>
> the following code illustrates a numeric problem with CP
> compiler, version BlackBox 1.4 unpatched. The comparison
> yields either TRUE or FALSE depending on the precision
> of the REAL number. (Try exchanging the order of the
> lines where the REAL variable is assigned). The language
> report does not say anything about such a mixed comparison
> (realVar = intVar). In the spirit of robustness I would
> rather prefer that this expression does not compile at all.
> ENTIER should be necessary, rather than relying on
> rounding the REAL variable in some implicit way.
>
> Excuse me if this was already patched.
>
> Wojtek Skulski skulski{([at]})nowhere.xy
>
> MODULE TestEqual;
> IMPORT StdLog;
> PROCEDURE Test*;
> VAR
> tst: BOOLEAN;
> r: REAL; long: LONGINT; int: INTEGER;
> BEGIN
> long := 1; int := 1;
> r := 1.000000000000000001; (* TRUE*)
> r := 1.0000000000001; (* FALSE*)
> tst := (r = long);
> StdLog.String("Real = long: ");
> StdLog.Bool (tst); StdLog.Ln;
> tst := (r = int);
> StdLog.String("Real = int: ");
> StdLog.Bool (tst); StdLog.Ln;
> END Test;
> END TestEqual.
>
> TestEqual.Test
>
> --------------------------------------------
>

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Received on Mon Feb 17 2003 - 18:29:13 UTC

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