1. Introduction
1. Introduction
The Concise Binary Object Representation (CBOR) [RFC7049] provides for the interchange of structured data without a requirement for a pre-agreed schema. [RFC7049] defines a basic set of data types as well as a tagging mechanism that enables extending the set of data types supported via an IANA registry.
Recently, a simple form of typed arrays of numeric data has received interest both in the Web graphics community [TypedArray] and in the JavaScript specification (see Section 22.2 (https://www.ecma-international.org/ecma-262/10.0/index.html#sec-typedarray-objects) of [ECMA-ES10]) as well as in corresponding implementations [ArrayBuffer].
Since these typed arrays may carry significant amounts of data, there is interest in interchanging them in CBOR without the need of lengthy conversion of each number in the array. This can also save space overhead with encoding a type for each element of an array.
This document defines a number of interrelated CBOR tags that cover these typed arrays, as well as additional tags for multi-dimensional and homogeneous arrays. It is intended as the reference document for the IANA registration of the tags defined.
Note that an application that generates CBOR with these tags has considerable freedom in choosing variants (e.g., with respect to endianness, embedded type (signed vs. unsigned), and number of bits per element) or whether a tag defined in this specification is used at all instead of more basic CBOR. In contrast to representation variants of single CBOR numbers, there is no representation that could be identified as "preferred". If deterministic encoding is desired in a CBOR-based protocol making use of these tags, the protocol has to define which of the encoding variants are used for each individual case.
1.1 Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
The term "byte" is used in its now-customary sense as a synonym for "octet". Where bit arithmetic is explained, this document uses familiar notation from the programming language C [C] (including C++14's 0bnnn binary literals [CPlusPlus]) with the exception of the operator "**", which stands for exponentiation.
The term "array" is used in a general sense in this document unless further specified. The term "classical CBOR array" describes an array represented with CBOR major type 4. A "homogeneous array" is an array of elements that are all the same type (the term is neutral as to whether that is a representation type or an application data model type).
The terms "big endian" and "little endian" are used to indicate a most significant byte first (MSB first) representation of integers and a least significant byte first (LSB first) representation, respectively.