github.com/go-xe2/third@v1.0.3/golang.org/x/text/internal/utf8internal/utf8internal.go (about)

     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  }