• Subject: Re: Integers-related trap in Lua 5.3
• From: "Soni L." <fakedme@...>
• Date: Wed, 18 May 2016 14:35:05 -0300

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On 18/05/16 02:28 PM, Roberto Ierusalimschy wrote:
```
```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:

It is a compile-time error if a decimal literal of type int is larger
than 2147483648 (2^31), or if the decimal literal 2147483648 appears
anywhere other than as the operand of the unary minus operator

Moreover, I don't think unsigned quantities solve the problem that
people are trying to solve here (unespected results from long
integers.) People that don't undestand what is going on don't
undertand unsigned quantities, either.

(I also think that people that don't undestand what is going on do not
write numbers like 10000000000000000000 in configuration files, so the
real problem seems more nit-picking than anything else to me, but I
may be wrong.)

-- Roberto

```
Correct me if I'm wrong but I think people have a problem with tonumber(), and, as tonumber() relies on Lua's number parsing rules, they want to "fix" the parser/lexer to fix tonumber(), with tonumber(read_user_input()) being the primary use-case.
```
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