[Cbor] Re: Two dup detection questions

[Rohan Mahy <[e-mail]>]

Hi Laurence,
Nice framing of the question.

On Tue, 2 Dec 2025, 20:50 Laurence Lundblade, <[e-mail]> wrote:

> Q: Why does dup detection operate on data mode values (and sorting
> doesn’t)?
>
> I think the answer is that the application makes use of the map keys in a
> critical way — to distinguish data items like a person’s last name from
> their shoe size. The application probably doesn’t have access to the
> serialized form of the map key. It doesn’t want access to it either — the
> point of CBOR is to serialize/deserialize data so applications don’t have
> to worry about it.
>
I agree that this seems to be the intent, but the spec language is
sufficiently vague I think it can cause inconsistent/ unpredictable
behavior that is the result of different encoders/decoders and the
languages they are written in. Not just different application logic


This contrasts to map sorting where the important thing is that they are in
> the same order, not so much what that order actually is.
>
>
>
> Q: Is -0.0 == +0.0 the only exception?


If deterministic serialization is used (regardless of which one or its
> name), then the only difference between binary comparison of the encoded
> forms and data model comparison is -0.0 == +0.0. Is that right? This is
> because in the general CBOR basic data model -0.0 != +0.0; and that is
> because they are not equal in the (implicit) IEEE 754 data model.

Almost, what about bigint demotion?

thanks,
-rohan


> Maybe these are kind of a “duh” question, but I think it helps for us to
> be all on the same page to keep the discussion grounded.
>
> I also kindly ask that you answer / discuss the question directly rather
> than say how your favorite flavor of CBOR works for these question. My
> questions are *only* about RFC 8949. I think that can also help the
> discussion grounded and progressing.
>
> LL
>
>
>
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