rss-tools @ master

// Copyright 2015 The Go Authors. All rights reserved.

// Use of this source code is governed by a BSD-style

// license that can be found in the LICENSE file.

// Package utf8internal contains low-level utf8-related constants, tables, etc.

// that are used internally by the text package.

package utf8internal

// The default lowest and highest continuation byte.

const (

	LoCB = 0x80 // 1000 0000

	HiCB = 0xBF // 1011 1111

)

// Constants related to getting information of first bytes of UTF-8 sequences.

const (

	// ASCII identifies a UTF-8 byte as ASCII.

	ASCII = as

	// FirstInvalid indicates a byte is invalid as a first byte of a UTF-8

	// sequence.

	FirstInvalid = xx

	// SizeMask is a mask for the size bits. Use use x&SizeMask to get the size.

	SizeMask = 7

	// AcceptShift is the right-shift count for the first byte info byte to get

	// the index into the AcceptRanges table. See AcceptRanges.

	AcceptShift = 4

	// The names of these constants are chosen to give nice alignment in the

	// table below. The first nibble is an index into acceptRanges or F for

	// special one-byte cases. The second nibble is the Rune length or the

	// Status for the special one-byte case.

	xx = 0xF1 // invalid: size 1

	as = 0xF0 // ASCII: size 1

	s1 = 0x02 // accept 0, size 2

	s2 = 0x13 // accept 1, size 3

	s3 = 0x03 // accept 0, size 3

	s4 = 0x23 // accept 2, size 3

	s5 = 0x34 // accept 3, size 4

	s6 = 0x04 // accept 0, size 4

	s7 = 0x44 // accept 4, size 4

)

// First is information about the first byte in a UTF-8 sequence.

var First = [256]uint8{

	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x00-0x0F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x10-0x1F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x20-0x2F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x30-0x3F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x40-0x4F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x50-0x5F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x60-0x6F

	as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, // 0x70-0x7F

	//   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x80-0x8F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0x90-0x9F

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xA0-0xAF

	xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xB0-0xBF

	xx, xx, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xC0-0xCF

	s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, s1, // 0xD0-0xDF

	s2, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s3, s4, s3, s3, // 0xE0-0xEF

	s5, s6, s6, s6, s7, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, xx, // 0xF0-0xFF

}

// AcceptRange gives the range of valid values for the second byte in a UTF-8

// sequence for any value for First that is not ASCII or FirstInvalid.

type AcceptRange struct {

	Lo uint8 // lowest value for second byte.

	Hi uint8 // highest value for second byte.

}

// AcceptRanges is a slice of AcceptRange values. For a given byte sequence b

//

//	AcceptRanges[First[b[0]]>>AcceptShift]

//

// will give the value of AcceptRange for the multi-byte UTF-8 sequence starting

// at b[0].

var AcceptRanges = [...]AcceptRange{

	0: {LoCB, HiCB},

	1: {0xA0, HiCB},

	2: {LoCB, 0x9F},

	3: {0x90, HiCB},

	4: {LoCB, 0x8F},

}