locale/utf2.4

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   5 .\" Paul Borman at Krystal Technologies.
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  35 .\"     @(#)utf2.4      8.1 (Berkeley) 6/4/93
  36 .\" $FreeBSD: src/lib/libc/locale/utf2.4,v 1.8.2.1 2001/03/06 16:45:58 ru Exp $
  37 .\"
  38 .Dd June 4, 1993
  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 The
  49 .Nm UTF2
  50 encoding is based on a proposed X-Open multibyte
  51 \s-1FSS-UCS-TF\s+1 (File System Safe Universal Character Set Transformation Format) encoding as used in
  52 .Sy "Plan 9 from Bell Labs" .
  53 Although it is capable of representing more than 16 bits,
  54 the current implementation is limited to 16 bits as defined by the
  55 Unicode Standard.
  56 .Pp
  57 .Nm UTF2
  58 representation is backwards compatible with ASCII, so 0x00-0x7f refer to the
  59 ASCII character set.  The multibyte encoding of runes between 0x0080 and 0xffff
  60 consist entirely of bytes whose high order bit is set.  The actual
  61 encoding is represented by the following table:
  62 .Bd -literal
  63 [0x0000 - 0x007f] [00000000.0bbbbbbb] -> 0bbbbbbb
  64 [0x0080 - 0x07ff] [00000bbb.bbbbbbbb] -> 110bbbbb, 10bbbbbb
  65 [0x0800 - 0xffff] [bbbbbbbb.bbbbbbbb] -> 1110bbbb, 10bbbbbb, 10bbbbbb
  66 .Ed
  67 .Pp
  68 If more than a single representation of a value exists (for example,
  69 0x00; 0xC0 0x80; 0xE0 0x80 0x80) the shortest representation is always
  70 used (but the longer ones will be correctly decoded).
  71 .Pp
  72 The final three encodings provided by X-Open:
  73 .Bd -literal
  74 [00000000.000bbbbb.bbbbbbbb.bbbbbbbb] ->
  75         11110bbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  76
  77 [000000bb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  78         111110bb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  79
  80 [0bbbbbbb.bbbbbbbb.bbbbbbbb.bbbbbbbb] ->
  81         1111110b, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb, 10bbbbbb
  82 .Ed
  83 .Pp
  84 which provides for the entire proposed ISO-10646 31 bit standard are currently
  85 not implemented.
  86 .Sh "SEE ALSO"
  87 .Xr mklocale 1 ,
  88 .Xr setlocale 3