utf8internal.go raw
1 // Copyright 2015 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 // Package utf8internal contains low-level utf8-related constants, tables, etc.
6 // that are used internally by the text package.
7 package utf8internal
8
9 // The default lowest and highest continuation byte.
10 const (
11 LoCB = 0x80 // 1000 0000
12 HiCB = 0xBF // 1011 1111
13 )
14
15 // Constants related to getting information of first bytes of UTF-8 sequences.
16 const (
17 // ASCII identifies a UTF-8 byte as ASCII.
18 ASCII = as
19
20 // FirstInvalid indicates a byte is invalid as a first byte of a UTF-8
21 // sequence.
22 FirstInvalid = xx
23
24 // SizeMask is a mask for the size bits. Use use x&SizeMask to get the size.
25 SizeMask = 7
26
27 // AcceptShift is the right-shift count for the first byte info byte to get
28 // the index into the AcceptRanges table. See AcceptRanges.
29 AcceptShift = 4
30
31 // The names of these constants are chosen to give nice alignment in the
32 // table below. The first nibble is an index into acceptRanges or F for
33 // special one-byte cases. The second nibble is the Rune length or the
34 // Status for the special one-byte case.
35 xx = 0xF1 // invalid: size 1
36 as = 0xF0 // ASCII: size 1
37 s1 = 0x02 // accept 0, size 2
38 s2 = 0x13 // accept 1, size 3
39 s3 = 0x03 // accept 0, size 3
40 s4 = 0x23 // accept 2, size 3
41 s5 = 0x34 // accept 3, size 4
42 s6 = 0x04 // accept 0, size 4
43 s7 = 0x44 // accept 4, size 4
44 )
45
46 // First is information about the first byte in a UTF-8 sequence.
47 var First = [256]uint8{
48 // 1 2 3 4 5 6 7 8 9 A B C D E F
49 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
50 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
51 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
52 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
53 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
54 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
55 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
56 as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
57 // 1 2 3 4 5 6 7 8 9 A B C D E F
58 xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
59 xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
60 xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
61 xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
62 xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
63 s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
64 s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
65 s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
66 }
67
68 // AcceptRange gives the range of valid values for the second byte in a UTF-8
69 // sequence for any value for First that is not ASCII or FirstInvalid.
70 type AcceptRange struct {
71 Lo uint8 // lowest value for second byte.
72 Hi uint8 // highest value for second byte.
73 }
74
75 // AcceptRanges is a slice of AcceptRange values. For a given byte sequence b
76 //
77 // AcceptRanges[First[b[0]]>>AcceptShift]
78 //
79 // will give the value of AcceptRange for the multi-byte UTF-8 sequence starting
80 // at b[0].
81 var AcceptRanges = [...]AcceptRange{
82 0: {LoCB, HiCB},
83 1: {0xA0, HiCB},
84 2: {LoCB, 0x9F},
85 3: {0x90, HiCB},
86 4: {LoCB, 0x8F},
87 }
88