lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

On 18/05/16 04:00 PM, Sean Conner wrote:
It was thus said that the Great Roberto Ierusalimschy once stated:
It was thus said that the Great Roberto Ierusalimschy once stated:
One problem with all proposed solutions is math.mininteger. The
lexer reads numbers without signal. (Several languages do the
same, e.g. C).  This means that -9223372036854775808 is read as
-(9223372036854775808) (a unary minus applied over a positive
constant). But 9223372036854775808 is not a valid integer, so it would
result in a float (or nil, or inf, or error). Whatever the choice, the
final value of -9223372036854775808 would not be an integer, despite
it being a valid integer.
   I haven't looked at the code, but couldn't the lexer read the minus sign
and set a flag. Then read in the number as an unsigned quantity and as long
as it's not a float (no decimal point, no 'e' or 'E', etc.) then check
against LLONG_MIN and LLONG_MAX? 9223372036854775808 *is* representable as
an unsigned quantity.
The lexer cannot distinguish between a "-9223372036854775808" in
"x = -9223372036854775808" and in "x = x-9223372036854775808". It
handles both the same way, so the only way is a minus and then
a constant. (As I said, this is a common thing in programming
languages; C and Java, for instance, have this same rule.) There
are work arounds, but they are work arounds... Java, for instance,
has an axplicit provision for that case:
   There are two cases here:

	x = x-9223372036854775808
	x = x--9223372036854775808

In the first case, the '-' is the operator and you are trying to subtract a
positive integer that exceeds the bounds for a positive integer (and then
"something happens" but that "something happens" is beyond the scope for
now).  In the second case, you have a '-' as an operator, and a '-' that is
part of the number (a unary operator).  So you end up with subtracting a
negative number, which *can* be represented as an integer.

   Or does the lexer not handle this like this at all?


Something tells me you're wrong about the second case :P

Disclaimer: these emails may be made public at any given time, with or without reason. If you don't agree with this, DO NOT REPLY.