locale/FreeBSD/utf2.4

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  35 .\"     @(#)utf2.4      8.1 (Berkeley) 6/4/93
  36 .\" $FreeBSD: src/lib/libc/locale/utf2.4,v 1.10 2002/10/10 22:56:18 tjr Exp $
  37 .\"
  38 .Dd October 11, 2002
  39 .Dt UTF2 4
  40 .Os
  41 .Sh NAME
  42 .Nm utf2
  43 .Nd "Universal character set Transformation Format encoding of runes
  44 .Sh SYNOPSIS
  45 .Nm ENCODING
  46 .Qq UTF2
  47 .Sh DESCRIPTION
  48 .Bf Em
  49 The UTF2 encoding has been deprecated in favour of UTF-8.
  50 .Ef
  51 New applications should not use UTF2.
  52 .Pp
  53 The
  54 .Nm UTF2
  55 encoding is based on a proposed X-Open multibyte
  56 \s-1FSS-UCS-TF\s+1 (File System Safe Universal Character Set Transformation Format) encoding as used in
  57 .Sy "Plan 9 from Bell Labs" .
  58 Although it is capable of representing more than 16 bits,
  59 the current implementation is limited to 16 bits as defined by the
  60 Unicode Standard.
  61 .Pp
  62 .Nm UTF2
  63 representation is backwards compatible with ASCII, so 0x00-0x7f refer to the
  64 ASCII character set.  The multibyte encoding of runes between 0x0080 and 0xffff
  65 consist entirely of bytes whose high order bit is set.  The actual
  66 encoding is represented by the following table:
  67 .Bd -literal
  68 [0x0000 - 0x007f] [00000000.0bbbbbbb] -> 0bbbbbbb
  69 [0x0080 - 0x07ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
  70 [0x0800 - 0xffff] [bbbbbbbb.bbbbbbbb] -> 1110bbbb, 10bbbbbb, 10bbbbbb
  71 .Ed
  72 .Pp
  73 If more than a single representation of a value exists (for example,
  74 0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always
  75 used (but the longer ones will be correctly decoded).
  76 .Pp
  77 The final three encodings provided by X-Open:
  78 .Bd -literal
  79 [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
  80         11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  81
  82 [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  83         111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  84
  85 [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  86         1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  87 .Ed
  88 .Pp
  89 which provides for the entire proposed ISO-10646 31 bit standard are currently
  90 not implemented.
  91 .Sh "SEE ALSO"
  92 .Xr mklocale 1 ,
  93 .Xr setlocale 3 ,
  94 .Xr utf8 5