Progression Bar

From: René A. Krywult <"René>
Date: Thu, 11 Dec 2003 11:17:06 +0100 (NFT)

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Content-type: text/plain

Helmut,

Just two questions:

1) Why did you choose to only link an integer to the view? There are at least three values that are interesting for the bar, namely min, cur and max (there's a good argument for the other properties, too, but even more for these three)? cur does not have a meaning aside from min and max, IMHO.

2) For all values of max >1207 and min = 0 and cur =max-1 a TRAP 20 happens in f.DrawRect at CtlsProgress.DrawBars, and size is negative!

I believe this comes from a calculation with INTEGERs greater than MAX(INTEGER). The following code shows the problem in a simplified manner:

MODULE PrivTestI;
IMPORT Out;
PROCEDURE Do*;
VAR
 min,max,cur:INTEGER;
BEGIN
        min:= MIN(INTEGER);
        max:=MAX(INTEGER);
        cur:=max+1;
        HALT(40);
END Do;
END PrivTestI.

I would have assumed that the line cur:=max+1; would produce a trap, but instead, cur is MIN(INTEGER)!

So my next try was cur:=MAX(INTEGER)+1, which leads to a compilation error (number too large). From this I assume that type ranges are not generally cyclic in nature, and the behavior in the above code sample is simply an error of the runtime environment. IMHO, this IS problematic, since there is no easy way to check violation of type boundaries at runtime. The results are therefor unpredictable. And even if there were a way to check the violation, this would mean that in EVERY case one uses calculations, one would also have to check boundary violations. This blurs the code.

The above behavior I tested in BB 1.3, and in BB 1.4beta, which I only use for information (Since I use 1.3, I have problems using code that was designed for 1.4. I use the beta to understand the differences between 1.3 and 1.4 only).

Rene


=============René A. Krywult
-------------------------------------------------
Lege, lege, relege, ora, labora et invenies
___________________________________





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Received on Thu Dec 11 2003 - 11:17:06 UTC