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UTF-9 and UTF-18 Efficient Transformation Formats of Unicode (RFC4042)

IP.com Disclosure Number: IPCOM000117115D
Original Publication Date: 2005-Apr-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 10 page(s) / 19K

Publishing Venue

Internet Society Requests For Comment (RFCs)

Related People

M. Crispin: AUTHOR

Abstract

ISO-10646 defines a large character set called the Universal Character Set (UCS), which encompasses most of the world's writing systems. The same set of codepoints is defined by Unicode, which further defines additional character properties and other implementation details. By policy of the relevant standardization committees, changes to Unicode and amendments and additions to ISO/IEC 646 track each other, so that the character repertoires and code point assignments remain in synchronization.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 14% of the total text.

Network Working Group                                         M. Crispin
Request for Comments: 4042                             Panda Programming
Category: Informational                                     1 April 2005


                           UTF-9 and UTF-18
              Efficient Transformation Formats of Unicode

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2005).

Abstract

   ISO-10646 defines a large character set called the Universal
   Character Set (UCS), which encompasses most of the world's writing
   systems.  The same set of codepoints is defined by Unicode, which
   further defines additional character properties and other
   implementation details.  By policy of the relevant standardization
   committees, changes to Unicode and amendments and additions to
   ISO/IEC 646 track each other, so that the character repertoires and
   code point assignments remain in synchronization.

   The current representation formats for Unicode (UTF-7, UTF-8, UTF-16)
   are not storage and computation efficient on platforms that utilize
   the 9 bit nonet as a natural storage unit instead of the 8 bit octet.

   This document describes a transformation format of Unicode that takes
   advantage of the nonet so that the format will be storage and
   computation efficient.

1.  Introduction

   A number of Internet sites utilize platforms that are not based upon
   the traditional 8-bit byte or octet.  One such platform is the PDP-
   10, which is based upon a 36-bit word.  On these platforms, it is
   wasteful to represent data in octets, since 4 bits are left unused in
   each word.  The 9-bit nonet is a much more sensible representation.

   Although these platforms support IETF standards, many of these
   platforms still utilize a text representation based upon the septet,


Crispin                      Informational                      [Page 1]
RFC 4042                    UTF-9 and UTF-18                1 April 2005


   which is only suitable for [US-ASCII] (although it has been used for
   various ISO 10646 national variants).

   To maximize international and multi-lingual interoperability, the IAB
   has recommended ([IAB-CHARACTER]) that [ISO-10646] be the default
   coded character set.

   Although other transformation formats of [UNICODE] exist, and
   conceivably can be used on nonet-oriented machines (most notably
   [UTF-8]), they suffer significant disadvantages:

      [UTF-8]
         requires one to three octets to represent codepoints in the
  ...