[Cbor] Re: I-D Action: draft-mcnally-deterministic-cbor-10.html

[Anders Rundgren <[e-mail]>]

On 2024-06-17 11:23, Wolf McNally wrote:
> Anders,
> 
>> On Jun 16, 2024, at 7:50 AM, Anders Rundgren <[e-mail]> wrote:
>>
>> Revised text proposal:
>>
>> 2.3 Numeric Reduction
>>     To provide deterministic encoding in platforms that do not separate integer
>>     and floating point values (like JavaScript), numbers must be canonicalized.
>>     Numeric reduction ensures that semantically equal numeric values (e.g. 2 and 2.0)
>>     are encoded into identical byte streams (e.g. 0x02) by encoding "Integral floating point values"
>>     (floating point values with a zero fractional part) as integers when possible.
>>
>> Since this is the essence of dCBOR, I would drop all other parts of dCBOR, since similar restrictions and limitations can be found in just about any other CBOR-using application as well.
> 
> This is *not* the "essence of dCBOR.” There is *nothing* platform-specific in the motivation or specification of dCBOR, not for JavaScript or any other execution environment.

Well, my wording was maybe not the best.  New try:

   Numeric reduction provides deterministic encoding of common number types which fits
   both systems that separate integer and floating point values (like Java) and those
   that do not (like JavaScript). Numeric reduction ensures that semantically equal
   numeric values (e.g. 2 and 2.0) are encoded into identical byte streams (e.g. 0x02)
   by encoding "Integral floating point values" (floating point values with a zero
   fractional part) as integers when possible.


> The motivation for numeric reduction is: to give the most common types of numeric values a *deterministic* serialization.

Right. This makes perfect sense in the scenario I just described.  However, if you put platform-native data types in CBOR wrappers or use type-specific write methods, preferred serialization à la CDE is a more logical choice [1,2,3].  Using Swift, I could even ditch the wrappers!

With respect to the "quality" of the determinism, I am not aware of any differences.


Anders

1] WG-adopted work-item
2] Simpler code
3] Preserves the self-describing nature of CBOR

> 
> That’s it.
> 
> No more no less.
> 
> Please stop mischaracterizing.
> 
> ~ Wolf