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Re: [Cbor] Announcement: draft-mcnally-deterministic-cbor-03

Carsten Bormann <cabo@tzi.org> Mon, 07 August 2023 16:12 UTC

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From: Carsten Bormann <cabo@tzi.org>
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Date: Mon, 07 Aug 2023 18:12:19 +0200
Cc: Wolf McNally <wolf@wolfmcnally.com>, cbor@ietf.org
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To: Joe Hildebrand <hildjj@cursive.net>
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Subject: Re: [Cbor] Announcement: draft-mcnally-deterministic-cbor-03
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On 2023-08-07, at 18:00, Joe Hildebrand <hildjj@cursive.net> wrote:
> 
> One more thing, there may need to be another note that says that the integer descriptors for complex types (array, map, tag, byte string, utf8 string) MUST follow the rules for mt 0/1.  It's implied strongly and probably difficult to implement any other way, but 
> might be worth mentioning.

Hi Joe,

descriptor is not a word we use in RFC 8949.
We have something that is used with all of these, which is by definition an unsigned integer: The argument [1].

The argument can represent any integral number between 0 and 2**64-1.

The argument is directly used as the mt0 value (the mt1 value is -argument-1, or, in C integer arithmetic, ~argument).  For mt2 and mt3, the argument gives the length of the string in bytes.  For mt4, the number of elements in the array.  mt5, number of pairs in the map.  mt6, the tag number.  mt7 is a bit more complicated.

So, by definition, the argument already behaves like an mt0, because mt0 is defined by the argument...

Grüße, Carsten

[1]: https://www.rfc-editor.org/rfc/rfc8949.html#name-specification-of-the-cbor-e

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