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[Cbor] Self Described CBOR - Little Endian

alex thompson <pierogitus@hotmail.com> Tue, 23 March 2021 04:50 UTC

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From: alex thompson <pierogitus@hotmail.com>
To: "cbor@ietf.org" <cbor@ietf.org>
Thread-Topic: Self Described CBOR - Little Endian
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Date: Tue, 23 Mar 2021 04:50:29 +0000
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Subject: [Cbor] Self Described CBOR - Little Endian
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​Given the prevalence of little endian hardware and the existence of the LE typed array tags it would be useful to opt-in to LE encoding of the additional information bytes as well. This would simplify decoders that are specific to LE platforms, particularly WebAssembly which is all LE and hasn’t defined a swap instruction.

The opt-in could be self described with tag 55798 (has the same non-unicode magic number characteristic as 55799). The beginning of a stream would default to BE so tag 55798 itself would appear as 0xd9d9f6. Then any following tags and descendant items would be LE.

For completeness, 55798 and 55799 could be nested within one another, switching the endianness as the decoder traverses a tree of items. Nested tags 24 and 63 would pass on their endianness to their embedded items. No effect on typed array tags 64-87.

It would be a breaking change for generic decoders since ignoring 55798 wouldn’t work as expected but I think the impact is very manageable and fits with CBOR’s stated goals of small code size and extensibility.

Alex

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