MIME GB2312 Standard GB 2312 (1980) Succeeded by GBK, GB 18030 | Alias(es) csGB2312 Language(s) zh | |
GB2312 is the registered internet name for a key official character set of the People's Republic of China, used for simplified Chinese characters. GB abbreviates Guojia Biaozhun (国家标准), which means national standard in Chinese. GB2312 (1980) has been superseded by GBK and GB18030, which include additional characters, but GB2312 is nonetheless still in widespread use.
Contents
While GB2312 covers over 99% of the characters of contemporary usage, historical texts and many names remain out of scope. GB2312 includes 6,763 Chinese characters (on two levels: the first is arranged by reading, the second by radical then number of strokes), along with symbols and punctuation, Japanese kana, the Greek and Cyrillic alphabets, Zhuyin, and a double-byte set of Pinyin letters with tone marks. 0.8% of all web pages use GB2312 in April 2016, a drop from 3.5% in January 2010.
There is an analogous character set known as GB/T 12345, closely related to GB2312, but with traditional character forms replacing simplified forms, and some extra 62 supplemental characters. GB-encoded fonts often come in pairs, one with the GB 2312 (simplified) character set and the other with the GB/T 12345 (traditional) character set.
Characters
Characters in GB2312 are arranged in a 94x94 grid (as in ISO 2022), and the two-byte codepoint of each character is expressed in the kuten (or quwei) form, which specifies a row (ku or qu) and the position of the character within the row (cell, ten or wei).
The rows (numbered from 1 to 94) contain characters as follows:
The rows 10-15 and 90-94 are unassigned.
For GB2312-80, it contains 682 signs and 6763 Chinese Charactes.
EUC-CN
EUC-CN is often used as the character encoding (i.e. for external storage) in programs that deal with GB2312, thus maintaining compatibility with ASCII. Two bytes are used to represent every character not found in ASCII. The value of the first byte is from 0xA1-0xF7 (161-247), while the value of the second byte is from 0xA1-0xFE (161-254). Since all of these ranges are beyond ASCII, like UTF-8, it is possible to check if a byte is part of a multi-byte construct when using EUC-CN, but not if a byte is first or last.
Compared to UTF-8, GB2312 (whether native or encoded in EUC-CN) is more storage efficient: while UTF-8 uses three bytes per CJK ideograph, GB2312 only uses two. However, GB2312 does not cover as many ideographs as Unicode does. And GB2312 is less time efficient, it requires division by 94 which is comparatively slow, while UTF-8 uses a fast shift operation.
To map the code points to bytes, add 158 (0x98) to the row number of the code point to form the high byte, and add 158 column number of the code point to form the low byte. The row number is the code point integer divided by 94, and the column the code point modulo 94.
For example, if you have the GB2312 code point 4566 ("外", which means foreign), the high byte will be 4566/94+158=206=0xCE, and the low byte will come from 4566%94+158=212=0xD4. So, the full encoding is 0xCED4=52948.
HZ
HZ is another encoding of GB2312 that is used mostly for Usenet postings.
Two implementations of GB2312
There are two implementations of GB2312 which differ in few code points.
The GBK/GB18030 subset is compatible with both GBK and GB18030; GB2312.TXT is the then-official implementation from ftp.unicode.org, which has been obsolete since August 2011 and missing as of September 2016. Even more vendor mappings existed.
As of 2015, Microsoft .Net Framework is using the subset. ICU, iconv-1.14, php-5.6, ActivePerl-5.20, Java 1.7 and Python 3.4 are using GB2312.TXT. Ruby 2.2 is compatible with both implementations; it internally converts the conflictive characters to the subset. W3C's technical recommendation specifies a GBK encoding to be inferred for streams labelled gb2312, which in turn uses a GB18030 decoder.