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Content-type: text/plain
> -----Original Message-----
> From: Campbell, Robert D (UK Edinburgh)
> [mailto:robert.d.campbell{([at]})nowhere.xy> Sent: Thursday, 2 December 2004 9:38 PM
> To: blackbox{([at]})nowhere.xy> Subject: CONST arithmetic
>
>
>
> I have some code:
>
> CONST
> arrayLen = 5;
> arrayMax = arrayLen - 1;
>
> VAR
> xyx : REAL;
>
> BEGIN
> xyz := 100. / arrayMax;
>
>
> Fine.
> But for a simple test case I set arraylen = 1.
> I get a compiler error 'division by zero'.
>
> This is not an error; my algorithm will work fine with
> xyz = INF.
>
I would have expected this to be handled OK by the compiler. It sounds
like a deficiency in its constant expression evaluation process.
> Even if I add
>
> IF arraylen > 1 THEN xyz := 100. / arrayMax END
>
> I still get a compiler error.
>
> Is this a restriction in the language, or the compiler, or ...?
>
> I thought that the compiler removed 'dead' code of the form:
>
> IF FALSE THEN ... END anyway.
>
I wouldn't have expected this to make any difference in this situation.
The compiler can't simply ignore what follows the 'IF FALSE THEN' It
actually has to parse what follows so that it knows when it has passed
all of the dead code. It is the parsing process which does the constant
calculations etc. Thus it will hit the same problem. Similarly if you
had any syntax errors in the dead code, these would be reported as well.
If the compiler does remove 'dead' code, (which is not a requirement of
the language), it is quite possible that it does it at a later stage,
once parsing has been completed and the code is being generated.
In the meantime, a workaround to this problem is to use a variable to
prevent the compiler attempting to evaluate the division calculation at
compile-time. e.g.
CONST
arrayLen = 1;
arrayMax = arrayLen - 1;
VAR
xyx: REAL;
aMax: INTEGER;
BEGIN
aMax := arrayMax;
xyz := 100.0 / aMax;
Regards,
Chris Burrows
CFB Software
http://www.cfbsoftware.com
info{([at]})nowhere.xy
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Received on Fri Dec 03 2004 - 00:06:32 UTC