EUC implements a system of 4 multibyte codesets. A multibyte character in the first codeset consists of len1 bytes starting with a byte in the range of 0x00 to 0x7f. To allow use of ASCII, len1 is always 1. A multibyte character in the second codeset consists of len2 bytes starting with a byte in the range of 0x80-0xff excluding 0x8e and 0x8f. A multibyte character in the third codeset consists of len3 bytes starting with the byte 0x8e. A multibyte character in the fourth codeset consists of len4 bytes starting with the byte 0x8f.
.Vt wchar_t encoding of EUC multibyte characters is dependent on the len and mask arguments. First, the bytes are moved into a
.Vt wchar_t as follows:
byte0 << ((lenN-1) * 8) | byte1 << ((lenN-2) * 8) | ... | bytelenN-1
The result is then ANDed with ~mask and ORed with maskN. Codesets 2 and 3 are special in that the leading byte (0x8e or 0x8f) is first removed and the lenN argument is reduced by 1.
For example, the ja_JP.eucJP locale has the following VARIABLE line:
VARIABLE 1 0x0000 2 0x8080 2 0x0080 3 0x8000 0x8080
Codeset 1 consists of the values 0x0000 - 0x007f.
Codeset 2 consists of the values who have the bits 0x8080 set.
Codeset 3 consists of the values 0x0080 - 0x00ff.
Codeset 4 consists of the values 0x8000 - 0xff7f excluding the values which have the 0x0080 bit set.
Notice that the global mask is set to 0x8080, this implies that from those 2 bits the codeset can be determined.