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87 lines
3.5 KiB
Go
87 lines
3.5 KiB
Go
// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package utf8internal contains low-level utf8-related constants, tables, etc.
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// that are used internally by the text package.
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package utf8internal
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// The default lowest and highest continuation byte.
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const (
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LoCB = 0x80 // 1000 0000
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HiCB = 0xBF // 1011 1111
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)
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// Constants related to getting information of first bytes of UTF-8 sequences.
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const (
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// ASCII identifies a UTF-8 byte as ASCII.
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ASCII = as
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// FirstInvalid indicates a byte is invalid as a first byte of a UTF-8
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// sequence.
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FirstInvalid = xx
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// SizeMask is a mask for the size bits. Use use x&SizeMask to get the size.
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SizeMask = 7
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// AcceptShift is the right-shift count for the first byte info byte to get
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// the index into the AcceptRanges table. See AcceptRanges.
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AcceptShift = 4
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// The names of these constants are chosen to give nice alignment in the
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// table below. The first nibble is an index into acceptRanges or F for
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// special one-byte cases. The second nibble is the Rune length or the
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// Status for the special one-byte case.
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xx = 0xF1 // invalid: size 1
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as = 0xF0 // ASCII: size 1
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s1 = 0x02 // accept 0, size 2
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s2 = 0x13 // accept 1, size 3
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s3 = 0x03 // accept 0, size 3
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s4 = 0x23 // accept 2, size 3
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s5 = 0x34 // accept 3, size 4
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s6 = 0x04 // accept 0, size 4
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s7 = 0x44 // accept 4, size 4
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)
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// First is information about the first byte in a UTF-8 sequence.
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var First = [256]uint8{
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// 1 2 3 4 5 6 7 8 9 A B C D E F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F
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as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F
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// 1 2 3 4 5 6 7 8 9 A B C D E F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF
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xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF
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xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF
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s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF
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s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF
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s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF
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}
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// AcceptRange gives the range of valid values for the second byte in a UTF-8
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// sequence for any value for First that is not ASCII or FirstInvalid.
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type AcceptRange struct {
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Lo uint8 // lowest value for second byte.
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Hi uint8 // highest value for second byte.
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}
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// AcceptRanges is a slice of AcceptRange values. For a given byte sequence b
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//
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// AcceptRanges[First[b[0]]>>AcceptShift]
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//
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// will give the value of AcceptRange for the multi-byte UTF-8 sequence starting
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// at b[0].
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var AcceptRanges = [...]AcceptRange{
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0: {LoCB, HiCB},
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1: {0xA0, HiCB},
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2: {LoCB, 0x9F},
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3: {0x90, HiCB},
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4: {LoCB, 0x8F},
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}
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