Re: The signs of literals

Hung-Ta Lin wrote in message 97-12-053...
> ...
>Would it be okay to change that grammar to:
>
> exp5 ::= [+|-] exp6
> exp6 ::= integer_literal | ...
>
> integer_literal ::= digit {digit}


This works just fine if you use:


exp5 ::= [+|-] exp5


You really have to think about the semantic meaning of these expressions,
though.


It would probably be odd to have "-32768" and "- 32768" mean different
things, but as another poster mentioned, if -32768 is the most negative
value you can put in an integer_literal, then 32767 is probably the highest
value you can put in an integer_literal, -(32768) would overflow.


If don't want to catch overflows of literals as errors, then you do not have
a problem if you do everything in the naive way:


3276*10 -> 32760
32760 + 8 -> -32768 //wrapped around here
-(-32768) -> -32768 //negating this value has no effect


so 32768 will wrap around to zero and - 32768 will evaluate to zero


--

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