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

"Edsko de Vries" <devriese@cs.tcd.ie> writes:


> our current definition for integer constant looks something like
>
> INT ([1-9][0-9]*)|0
>
> In particular, note that it does not allow for an (optional) "+" or "-"
> at the start of the integer. In other words, "-" is treated as a unary
> operator, rather than as part of the number.
>
> 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.
>
> At the moment, I have added a new rule to the lexer that matches
> this exact number, which solves the problem - but it's a hack..


One solution is to let the lexer keep the number as a string and
handle unary minus applied to a constant in the parser (at this time
converting the string to a number). Or you can use a bignum package
in the compiler, only converting to machine integers when you generate
code.


                Torben

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