Re: 1 - 1, 1 -1, 1-1, 1 - -1 and -2147483648

Edsko de Vries wrote:


> I have a question regarding lexical analysis. I recently came across a
> bug in our lexical analyser in phc (www.phpcompiler.org), that I am
> unsure how to solve. This is the problem: our current definition for
> integer constant looks something like


(snip)


> This works fine, with the sole exception of the number "-2147483648".
> The problem is, of course, overflow: -2147483648 is a valid negative
> number (assuming 32-bit numbers), but the integer 2147483648 is _not_ a
> valid positive number. Thus, the above method of dealing with "-" as a
> unary operator breaks down.


(snip)


Look at the language definition. C allows only positive constants
and unary operators, as you say, though a constant expression might
have the value -2147483648.


Fortran allows only positive constants in expressions, but optionally
signed constants in DATA statements. It might not be required, but I
believe most compilers will allow the maximum negative number in a DATA
statement.


-- glen

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