mirror of
https://github.com/autc04/Retro68.git
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395 lines
8.6 KiB
Go
395 lines
8.6 KiB
Go
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// Copyright 2009 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 utf8 implements functions and constants to support text encoded in
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// UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.
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package utf8
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import "unicode" // only needed for a couple of constants
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// Numbers fundamental to the encoding.
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const (
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RuneError = unicode.ReplacementChar // the "error" Rune or "replacement character".
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RuneSelf = 0x80 // characters below Runeself are represented as themselves in a single byte.
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UTFMax = 4 // maximum number of bytes of a UTF-8 encoded Unicode character.
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)
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const (
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t1 = 0x00 // 0000 0000
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tx = 0x80 // 1000 0000
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t2 = 0xC0 // 1100 0000
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t3 = 0xE0 // 1110 0000
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t4 = 0xF0 // 1111 0000
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t5 = 0xF8 // 1111 1000
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maskx = 0x3F // 0011 1111
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mask2 = 0x1F // 0001 1111
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mask3 = 0x0F // 0000 1111
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mask4 = 0x07 // 0000 0111
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rune1Max = 1<<7 - 1
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rune2Max = 1<<11 - 1
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rune3Max = 1<<16 - 1
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rune4Max = 1<<21 - 1
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)
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func decodeRuneInternal(p []byte) (r rune, size int, short bool) {
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n := len(p)
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if n < 1 {
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return RuneError, 0, true
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}
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c0 := p[0]
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// 1-byte, 7-bit sequence?
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if c0 < tx {
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return rune(c0), 1, false
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}
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// unexpected continuation byte?
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if c0 < t2 {
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return RuneError, 1, false
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}
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// need first continuation byte
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if n < 2 {
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return RuneError, 1, true
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}
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c1 := p[1]
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if c1 < tx || t2 <= c1 {
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return RuneError, 1, false
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}
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// 2-byte, 11-bit sequence?
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if c0 < t3 {
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r = rune(c0&mask2)<<6 | rune(c1&maskx)
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if r <= rune1Max {
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return RuneError, 1, false
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}
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return r, 2, false
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}
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// need second continuation byte
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if n < 3 {
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return RuneError, 1, true
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}
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c2 := p[2]
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if c2 < tx || t2 <= c2 {
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return RuneError, 1, false
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}
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// 3-byte, 16-bit sequence?
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if c0 < t4 {
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r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
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if r <= rune2Max {
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return RuneError, 1, false
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}
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return r, 3, false
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}
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// need third continuation byte
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if n < 4 {
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return RuneError, 1, true
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}
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c3 := p[3]
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if c3 < tx || t2 <= c3 {
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return RuneError, 1, false
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}
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// 4-byte, 21-bit sequence?
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if c0 < t5 {
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r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
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if r <= rune3Max {
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return RuneError, 1, false
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}
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return r, 4, false
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}
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// error
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return RuneError, 1, false
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}
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func decodeRuneInStringInternal(s string) (r rune, size int, short bool) {
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n := len(s)
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if n < 1 {
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return RuneError, 0, true
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}
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c0 := s[0]
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// 1-byte, 7-bit sequence?
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if c0 < tx {
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return rune(c0), 1, false
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}
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// unexpected continuation byte?
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if c0 < t2 {
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return RuneError, 1, false
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}
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// need first continuation byte
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if n < 2 {
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return RuneError, 1, true
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}
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c1 := s[1]
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if c1 < tx || t2 <= c1 {
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return RuneError, 1, false
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}
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// 2-byte, 11-bit sequence?
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if c0 < t3 {
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r = rune(c0&mask2)<<6 | rune(c1&maskx)
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if r <= rune1Max {
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return RuneError, 1, false
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}
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return r, 2, false
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}
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// need second continuation byte
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if n < 3 {
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return RuneError, 1, true
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}
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c2 := s[2]
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if c2 < tx || t2 <= c2 {
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return RuneError, 1, false
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}
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// 3-byte, 16-bit sequence?
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if c0 < t4 {
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r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
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if r <= rune2Max {
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return RuneError, 1, false
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}
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return r, 3, false
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}
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// need third continuation byte
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if n < 4 {
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return RuneError, 1, true
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}
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c3 := s[3]
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if c3 < tx || t2 <= c3 {
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return RuneError, 1, false
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}
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// 4-byte, 21-bit sequence?
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if c0 < t5 {
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r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
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if r <= rune3Max {
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return RuneError, 1, false
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}
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return r, 4, false
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}
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// error
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return RuneError, 1, false
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}
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// FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
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// An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
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func FullRune(p []byte) bool {
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_, _, short := decodeRuneInternal(p)
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return !short
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}
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// FullRuneInString is like FullRune but its input is a string.
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func FullRuneInString(s string) bool {
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_, _, short := decodeRuneInStringInternal(s)
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return !short
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}
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// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and its width in bytes.
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// If the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
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func DecodeRune(p []byte) (r rune, size int) {
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r, size, _ = decodeRuneInternal(p)
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return
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}
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// DecodeRuneInString is like DecodeRune but its input is a string.
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// If the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
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func DecodeRuneInString(s string) (r rune, size int) {
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r, size, _ = decodeRuneInStringInternal(s)
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return
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}
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// DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and its width in bytes.
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// If the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
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func DecodeLastRune(p []byte) (r rune, size int) {
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end := len(p)
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if end == 0 {
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return RuneError, 0
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}
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start := end - 1
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r = rune(p[start])
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if r < RuneSelf {
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return r, 1
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}
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// guard against O(n^2) behavior when traversing
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// backwards through strings with long sequences of
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// invalid UTF-8.
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lim := end - UTFMax
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if lim < 0 {
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lim = 0
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}
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for start--; start >= lim; start-- {
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if RuneStart(p[start]) {
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break
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}
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}
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if start < 0 {
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start = 0
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}
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r, size = DecodeRune(p[start:end])
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if start+size != end {
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return RuneError, 1
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}
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return r, size
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}
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// DecodeLastRuneInString is like DecodeLastRune but its input is a string.
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// If the encoding is invalid, it returns (RuneError, 1), an impossible result for correct UTF-8.
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func DecodeLastRuneInString(s string) (r rune, size int) {
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end := len(s)
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if end == 0 {
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return RuneError, 0
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}
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start := end - 1
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r = rune(s[start])
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if r < RuneSelf {
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return r, 1
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}
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// guard against O(n^2) behavior when traversing
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// backwards through strings with long sequences of
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// invalid UTF-8.
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lim := end - UTFMax
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if lim < 0 {
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lim = 0
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}
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for start--; start >= lim; start-- {
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if RuneStart(s[start]) {
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break
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}
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}
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if start < 0 {
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start = 0
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}
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r, size = DecodeRuneInString(s[start:end])
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if start+size != end {
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return RuneError, 1
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}
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return r, size
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}
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// RuneLen returns the number of bytes required to encode the rune.
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func RuneLen(r rune) int {
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switch {
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case r <= rune1Max:
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return 1
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case r <= rune2Max:
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return 2
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case r <= rune3Max:
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return 3
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case r <= rune4Max:
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return 4
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}
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return -1
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}
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// EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
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// It returns the number of bytes written.
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func EncodeRune(p []byte, r rune) int {
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// Negative values are erroneous. Making it unsigned addresses the problem.
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if uint32(r) <= rune1Max {
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p[0] = byte(r)
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return 1
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}
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if uint32(r) <= rune2Max {
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p[0] = t2 | byte(r>>6)
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p[1] = tx | byte(r)&maskx
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return 2
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}
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if uint32(r) > unicode.MaxRune {
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r = RuneError
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}
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if uint32(r) <= rune3Max {
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p[0] = t3 | byte(r>>12)
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p[1] = tx | byte(r>>6)&maskx
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p[2] = tx | byte(r)&maskx
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return 3
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}
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p[0] = t4 | byte(r>>18)
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p[1] = tx | byte(r>>12)&maskx
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p[2] = tx | byte(r>>6)&maskx
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p[3] = tx | byte(r)&maskx
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return 4
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}
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// RuneCount returns the number of runes in p. Erroneous and short
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// encodings are treated as single runes of width 1 byte.
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func RuneCount(p []byte) int {
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i := 0
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var n int
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for n = 0; i < len(p); n++ {
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if p[i] < RuneSelf {
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i++
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} else {
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_, size := DecodeRune(p[i:])
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i += size
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}
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}
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return n
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}
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// RuneCountInString is like RuneCount but its input is a string.
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func RuneCountInString(s string) (n int) {
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for _ = range s {
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n++
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}
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return
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}
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// RuneStart reports whether the byte could be the first byte of
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// an encoded rune. Second and subsequent bytes always have the top
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// two bits set to 10.
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func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
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// Valid reports whether p consists entirely of valid UTF-8-encoded runes.
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func Valid(p []byte) bool {
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i := 0
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for i < len(p) {
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if p[i] < RuneSelf {
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i++
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} else {
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_, size := DecodeRune(p[i:])
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if size == 1 {
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// All valid runes of size of 1 (those
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// below RuneSelf) were handled above.
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// This must be a RuneError.
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return false
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}
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i += size
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}
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}
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return true
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}
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// ValidString reports whether s consists entirely of valid UTF-8-encoded runes.
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func ValidString(s string) bool {
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for i, r := range s {
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if r == RuneError {
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// The RuneError value can be an error
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// sentinel value (if it's size 1) or the same
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// value encoded properly. Decode it to see if
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// it's the 1 byte sentinel value.
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_, size := DecodeRuneInString(s[i:])
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if size == 1 {
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return false
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}
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}
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}
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return true
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}
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