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

[Anthony Liguori <anthony@codemonkey.ws>]

On 05/23/2011 09:02 AM, Luiz Capitulino wrote:
> On Mon, 23 May 2011 08:50:55 -0500
> Anthony Liguori<anthony@codemonkey.ws>  wrote:
>
>>>> 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.
>
> Python json works just fine:
>
>>>> import json
>>>> json.dumps(9223372036854775807)
> '9223372036854775807'
>>>> json.loads('9223372036854775807')
> 9223372036854775807

Python integers use BigNumbers transparently when necessary.  That's 
what happening here.

There's a strong treatment of Python's behavior at 
http://deron.meranda.us/python/comparing_json_modules/numbers

Regards,

Anthony Liguori