Hello,
Another question following up, how about the sign character for hex
and oct integers? Is it necessary, should it be discarded?
intLit = decimalLit | octalLit | hexLit
decimalLit = ( "1" … "9" ) { decimalDigit }
octalLit = "0" { octalDigit }
hexLit = "0" ( "x" | "X" ) hexDigit { hexDigit }
constant = fullIdent | ( [ "-" | "+" ] intLit ) | ( [ "-" | "+" ]
floatLit ) | strLit | boolLit
https://developers.google.com/protocol-buffers/docs/reference/proto2-spec#integer_literals
https://developers.google.com/protocol-buffers/docs/reference/proto2-spec#constant
For instance, I am fairly certain the sign character is encoded in a
hex encoded integer. Not sure about octal, but I imagine that it is
fairly consistent.
Case in point, the value 107026150751750362 gets encoded as
0X17C3BB7913C48DA (upper-case). Whereas it's negative counterpart,
-107026150751750362, really does get encoded as 0xFE83C4486EC3B726.
Signage included, if memory serves.
In these cases, I think the sign bit falls in the "optional" category?
Cheers, thanks,
Michael
On Sun, Nov 11, 2018 at 10:56 AM Josh Humphries <[email protected]> wrote:
>
> For the case of zero by itself, per the spec, it will be parsed as an octal
> literal with value zero -- so functionally equivalent to a decimal literal
> with value zero. And for values with multiple digits, a leading zero means it
> is an octal literal. Decimal values will not have a leading zero.
>
> ----
> Josh Humphries
> [email protected]
>
>
> On Sat, Nov 10, 2018 at 10:16 PM Michael Powell <[email protected]> wrote:
>>
>> Hello,
>>
>> I think 0 can be a decimal-lit, don't you think? However, the spec
>> reads as follows:
>>
>> intLit = decimalLit | octalLit | hexLit
>> decimalLit = ( "1" … "9" ) { decimalDigit }
>> octalLit = "0" { octalDigit }
>> hexLit = "0" ( "x" | "X" ) hexDigit { hexDigit }
>>
>> Is there a reason, semantically speaking, why decimal must be greater
>> than 0? And that's not including a plus/minus sign when you factor in
>> constants.
>>
>> Of course, parsing, order matters, similar as with the escape
>> character phrases in the string-literal:
>>
>> hex-lit | oct-lit | dec-lit
>>
>> And so on, since you have to rule out 0x\d+ for hex, followed by 0\d* ...
>>
>> Actually, now that I look at it "0" (really, "decimal" 0) is lurking
>> in the oct-lit phrase.
>>
>> Kind of a grammatical nit-pick, I know, but I just wanted to be clear
>> here. Seems like a possible source of confusion if you aren't paying
>> careful attention.
>>
>> Thoughts?
>>
>> Best regards,
>>
>> Michael Powell
>>
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