Re: [Qemu-devel] [PATCH] qemu: json: Fix parsing of integers >= 0x8000000000000000

[Anthony Liguori <anthony@codemonkey.ws>]

>> The actual value of the alert will surprise you :-)
>>
>> Integers in Javascript are actually represented as doubles
>> internally which means that integer constants are only accurate up
>> to 52 bits.
>>
>> So really, we should cap integers at 32-bit :-/
>>
>> Have I mentioned recently that I really dislike JSON...
>
> NB, I am distinguishing between JSON the generic specification and
> JSON as implemented in web browsers. JSON the specification has *no*
> limitation on integers.

The spec has no notion of integers at all.  Here's the relevant text. 
Note that the BNF only has a single entry point for numbers.  It does 
not distinguish between integers and floating point numbers.  Also, the 
only discussion of valid numbers is about whether the number can be 
represented as a rational number.  I think the only way to read the spec 
here is that *all* numbers are meant to be represented as floating point 
numbers.

Regards,

Anthony Liguori

2.4.  Numbers

    The representation of numbers is similar to that used in most
    programming languages.  A number contains an integer component that
    may be prefixed with an optional minus sign, which may be followed by
    a fraction part and/or an exponent part.

    Octal and hex forms are not allowed.  Leading zeros are not allowed.

    A fraction part is a decimal point followed by one or more digits.

    An exponent part begins with the letter E in upper or lowercase,
    which may be followed by a plus or minus sign.  The E and optional
    sign are followed by one or more digits.

    Numeric values that cannot be represented as sequences of digits
    (such as Infinity and NaN) are not permitted.


          number = [ minus ] int [ frac ] [ exp ]

          decimal-point = %x2E       ; .

          digit1-9 = %x31-39         ; 1-9

          e = %x65 / %x45            ; e E

          exp = e [ minus / plus ] 1*DIGIT

          frac = decimal-point 1*DIGIT

          int = zero / ( digit1-9 *DIGIT )

          minus = %x2D               ; -

          plus = %x2B                ; +

          zero = %x30                ; 0