1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
|
.TH UTF 6
.SH NAME
UTF, Unicode, ASCII \- character set and format
.SH DESCRIPTION
The Inferno character set and representation are
based on the Unicode Standard and on the ISO multibyte
.SM UTF-8
encoding (Universal Character
Set Transformation Format, 8 bits wide).
The Unicode Standard represents its characters in 16
bits;
.SM UTF-8
represents such
values in an 8-bit byte stream.
Throughout this manual,
.SM UTF-8
is shortened to
.SM UTF.
.PP
Internally, programs store individual Unicode characters as 16-bit values.
However, any external manifestation of textual information,
in files or at the interface between programs, uses the
machine-independent, byte-stream encoding called
.SM UTF.
.PP
.SM UTF
is designed so the 7-bit
.SM ASCII
set (values hexadecimal 00 to 7F),
appear only as themselves
in the encoding.
Characters with values above 7F appear as sequences of two or more
bytes with values only from 80 to FF.
.PP
The
.SM UTF
encoding of the Unicode Standard is backward compatible with
.SM ASCII\c
: Inferno programs handle
.SM ASCII
text, as well as uninterpreted byte streams, without special arrangement.
However, programs that perform semantic processing on
characters must convert from
.SM UTF
to Unicode
in order to work properly with non-\c
.SM ASCII
input.
Normally, all necessary conversions are done by the Limbo compiler
and execution environment, but sometimes more is necessary, such
as when a program receives
.SM UTF
input one byte at a time;
see
.IR sys-byte2char (2)
for routines to handle such processing.
.PP
Letting numbers be binary,
a Unicode character x
is converted to a multibyte
.SM UTF
sequence
as follows:
.EX
01. x in [00000000.0bbbbbbb] \(-> 0bbbbbbb
10. x in [00000bbb.bbbbbbbb] \(-> 110bbbbb, 10bbbbbb
11. x in [bbbbbbbb.bbbbbbbb] \(-> 1110bbbb, 10bbbbbb, 10bbbbbb
.EE
.PP
Conversion 01 provides a one-byte sequence that spans the
.SM ASCII
character set in a compatible way.
Conversions 10 and 11 represent higher-valued characters
as sequences of two or three bytes with the high bit set.
Inferno does not support the 4-, 5-, and 6-byte sequences proposed by X-Open.
When there are multiple ways to encode a value, for example rune 0,
the shortest encoding is used.
.PP
In the inverse mapping,
any sequence except those described above
is incorrect and is converted to the Unicode value of hexadecimal 0080.
.SH "SEE ALSO"
.IR sys-byte2char (2),
.IR "The Unicode Standard" .
|
