Re: [Json] I-JSON Topic #5: Numbers

[Carsten Bormann <[e-mail]>]

On 27 May 2014, at 19:52, Matt Miller <[e-mail]> wrote:

> Is your suggestion then to leave the text as-is?  Or can you provide
> specific text to include?

As I said, the second half of the proposed addition does add clarity:

»Furthermore, an I-JSON sender MUST NOT expect a receiver to treat an integer whose absolute value is greater than 9007199254740992 as an exact value.«

To be able to attach this right to the first paragraph of 2.2, maybe s/Furthermore/In particular/.
Also add the suggestion to call out that 9007199254740992 is 2**53:

   Software which implements IEEE 754-2008 binary64 (double precision)
   numbers [IEEE754] is generally available and widely used.
   Implementations which generate I-JSON messages MUST NOT assume that
   receiving implementations can process numeric values with greater
   magnitude or precision than provided by those numbers.  I-JSON
   messages SHOULD NOT include numbers which express greater magnitude
   or precision than an IEEE 754 double precision number provides, for
   example 1E400 or 3.141592653589793238462643383279.
   ➧ In particular, an I-JSON sender MUST NOT expect a receiver to treat
   an integer whose absolute value is greater than 9007199254740992 (i.e., 
   that is outside the range [-2**53, 2**53], where ** stands for exponentiation)
   as an exact value.

This then leads well into the next paragraph:

   For applications such as cryptography, where much larger numbers are
   reasonably required, it is RECOMMENDED to encode them in JSON string
   values.  This requires that the receiving program understand the
   intended semantic of the value.

Maybe s/where…are/where exact interchange of…is/ in there for even more clarity.

Grüße, Carsten