Системы кодирования символов восточноазиатских языков (Sistemy kodirovaniya simvolov vostochnoaziatskikh yazykov)

System of East Asian character encodings

Extended Unix Code (EUC) is a multibyte character encoding system used primarily for Japanese, Korean, and simplified Chinese (characters). The most commonly used EUC codes are variable length encodings with a character belonging to an ISO/IEC 646 compliant coded character set (such as ASCII) taking one byte, and a character belonging to a 94×94 coded character set (such as GB 2312) represented in two bytes. The EUC CN form of GB 2312 and EUC KR are examples of such two byte EUC codes. EUC JP includes characters represented by up to three bytes, including an initial , whereas a single character in EUC TW can take up to four bytes. Modern applications are more likely to use UTF 8, which supports all of the glyphs of the EUC codes, and more, and is generally more portable with fewer vendor deviations and errors. EUC is however still very popular, especially EUC KR for South Korea.

The ISO 2022 based variable length encoding described above is sometimes referred to as the EUC packed format, which is the encoding format usually labeled as EUC. However, internal processing of EUC data may make use of a fixed length transformation format called the EUC complete two byte format. This represents: Only the packed format is included in the WHATWG Encoding Standard used by HTML5.

EUC CN which encodes GB 2312 the same way as EUC CN, but deviates from the EUC structure by extending the lead byte range back to 0x8C, adding 31 IBM selected characters in 0x8CE0 through 0x8CFE and adding 1880 user defined characters with lead bytes 0x8D through 0xA0. IBM code page 1383 (CCSID 1383) comprises the single byte code page 367 and the double byte code page 1382 (CPGID 1382 as CCSID 1382), which differs by conforming to the EUC structure, adding the 31 IBM selected characters in 0xFEE0 through 0xFEFE instead, and including only 1360 user defined characters, interspersed in the positions not used by GB 2312. The alternative CCSID 5479 is used for the pure EUC CN code page: it uses CCSID 9574 as its double byte set, which uses CPGID 1382 but excludes the IBM selected and user defined characters.

GBK is an extension to GB 2312. It defines an extended form of the EUC CN encoding capable of representing a larger array of CJK characters sourced largely from Unicode 1.1, including traditional Chinese characters and characters used only in Japanese. It is not, however, a true EUC code, because ASCII bytes may appear as trail bytes (and C1 bytes, not limited to the single shifts, may appear as lead or trail bytes), due to a larger encoding space being required. Variants of GBK are implemented by Windows code page 936 (the Microsoft Windows code page for simplified Chinese), and by IBM's code page 1386. The Unicode based GB 18030 character encoding defines an extension of GBK capable of encoding the entirety of Unicode. However, Unicode encoded as GB 18030 is a variable length encoding which may use up to four bytes per character, due to an even larger encoding space being required. Being an extension of GBK, it is a superset of EUC CN but is not itself a true EUC code. Being a Unicode encoding, its repertoire is identical to that of other Unicode transformation formats such as UTF 8.

Other EUC CN variants deviating from the EUC mechanism include the Mac OS Chinese Simplified script (known as Code page 10008 or x mac chinesesimp). It uses the bytes 0x80, 0x81, 0x82, 0xA0, 0xFD, 0xFE, and 0xFF for the U with umlaut (ü), two special font metric characters, the non breaking space, the copyright sign (©), the trademark sign (™) and the ellipsis ( ) respectively. This differs in what is regarded as a single byte character versus the first byte of a two byte character from both EUC (where, of those, 0xFD and 0xFE are defined as lead bytes) and GBK (where, of those, 0x81, 0x82, 0xFD and 0xFE are defined as lead bytes). This use of 0xA0, 0xFD, 0xFE and 0xFF matches Apple's Shift JIS variant. Besides these changes to the lead byte range, the other distinctive feature of the double byte portion of Mac OS Chinese Simplified is the inclusion of two extensions to the basic GB 2312 80 set in rows 6 and 8. and both extensions are included by GB 18030 (the successor to GB 2312).

A common extension of EUC KR is the Unified Hangul Code (, or ), which is the default Korean codepage on Microsoft Windows. It is given the code page number 949 by Microsoft, and 1261 or 1363 by IBM. IBM's code page 949 is a different, unrelated, EUC KR extension. Unified Hangul Code extends EUC KR by using codes that do not conform to the EUC structure to incorporate additional syllable blocks, completing the coverage of the composed syllable blocks available in Johab and Unicode. The W3C/WHATWG Encoding Standard used by HTML5 incorporates the Unified Hangul Code extensions into its definition of EUC KR.

Other encodings incorporating EUC KR as a subset include the Mac OS Korean script (known as Code page 10003 or x mac korean), Many of these characters do not have exact Unicode mappings, and Apple software maps these cases variously to combining sequences, to approximate mappings with an appended private use character as a modifier for round trip purposes, or to private use characters. Apple also uses certain single byte codes outside of the EUC KR plane for additional characters: 0x80 for a required space, 0x81 for a won sign (₩), 0x82 for an en dash (–), 0x83 for a copyright sign (©), 0x84 for a wide underscore (＿) and 0xFF for an ellipsis ( ). More recent editions of the standard extend the EUC representation with characters using non EUC two byte codes, in a similar manner to Unified Hangul Code.

Although certain single byte encodings such as the ISO/IEC 8859 series technically conform to the EUC structure, they are rarely labeled as EUC. However, is used on Solaris as a label for TIS 620.