Authors: Tom Bishop (tbishop@wenlin.com) and Richard Cook (rscook@wenlin.com).
Updated October, 2009.
Please Note: This is not a finalized specification. It is still at the "draft proposal" stage and may change.
The name of this specification is "UCS-E".
UCS-E enables extension of the Universal Character Set to support more than 9x1018 (nine times ten to the eighteenth power) characters, with code points up to U+7FFFFFFFFFFFFFFF. It is a member of the UCS-X family of specifications. It provides three encoding forms, UTF-E-8, UTF-E-16, and UTF-E-32, which are compatible extensions of UTF-8, UTF-16, and UTF-32, respectively.
UCS-E preserves and extends all the useful properties of UCS-G.
The set of UCS-E code points is the range U+0000..U+7FFFFFFFFFFFFFFF (fifteen F's). The number of code points is 263. As in Unicode, U+D800..U+DFFF (211 = 2,048 "surrogate code points") are excluded from the set of USV (UCS scalar values). Hence, the number of UCS-E scalar values is (exactly) 263 - 211 = 9,223,372,036,854,773,760 = (approximately) 9x1018 (nine quintillion).
UCS-E specifies three encoding forms (using 8-bit, 16-bit, and 32-bit units) that each associate a unique code with each USV. Detailed specifications are provided for the three encoding forms. Please see:
USV = U+0041 (the letter 'A') UTF-E-8 = 41 UTF-E-16 = 0041 UTF-E-32 = 00000041 USV = U+5B57 (the Chinese/Japanese/Korean character '字') UTF-E-8 = E5 AD 97 UTF-E-16 = 5B57 UTF-E-32 = 00005B57 USV = U+10FFFF (the last USV in the Unicode Standard) UTF-E-8 = F4 8F BF BF UTF-E-16 = DBFF DFFF UTF-E-32 = 0010FFFF USV = U+110000 (the first USV beyond the U+10FFFF limit) UTF-E-8 = F4 90 80 80 UTF-E-16 = DC04 DE80 DE00 UTF-E-32 = 00110000 USV = U+7FFFFFFF (the last USV in the original ISO 10646 standard) UTF-E-8 = FD BF BF BF BF BF UTF-E-16 = DD0F DFFF DFFF DFFF UTF-E-32 = 7FFFFFFF USV = U+80000000 (the first USV beyond the original ISO 10646) UTF-E-8 = FE 82 80 80 80 80 80 UTF-E-16 = DD10 DE00 DE00 DE00 UTF-E-32 = 80000000 USV = U+123456789 UTF-E-8 = FE 84 A3 91 96 9E 89 UTF-E-16 = DD24 DED1 DEB3 DF89 UTF-E-32 = F0000012 E3456789 USV = U+7FFFFFFFFFFFFFFF (the last USV supported by UCS-E) UTF-E-8 = FF 80 87 BF BF BF BF BF BF BF BF BF BF UTF-E-16 = DDF0 DFFF DFFF DFFF DFFF DFFF DFFF DFFF UTF-E-32 = FF00007F EFFFFFFF EFFFFFFF
More examples are shown in the individual specifications for UTF-E-8, UTF-E-16, and UTF-E-32.
The following graph compares the code lengths of UTF-E-8, UTF-E-16, and UTF-E-32. Note that each of the three forms is most efficient for certain ranges, and overall efficiency is similar.
For implementation, applications, references, etc., please see the UCS-X page.
