1 // Copyright 2016 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 runtime 6 7 // Numbers fundamental to the encoding. 8 const ( 9 runeError = '\uFFFD' // the "error" Rune or "Unicode replacement character" 10 runeSelf = 0x80 // characters below Runeself are represented as themselves in a single byte. 11 maxRune = '\U0010FFFF' // Maximum valid Unicode code point. 12 ) 13 14 // Code points in the surrogate range are not valid for UTF-8. 15 const ( 16 surrogateMin = 0xD800 17 surrogateMax = 0xDFFF 18 ) 19 20 const ( 21 t1 = 0x00 // 0000 0000 22 tx = 0x80 // 1000 0000 23 t2 = 0xC0 // 1100 0000 24 t3 = 0xE0 // 1110 0000 25 t4 = 0xF0 // 1111 0000 26 t5 = 0xF8 // 1111 1000 27 28 maskx = 0x3F // 0011 1111 29 mask2 = 0x1F // 0001 1111 30 mask3 = 0x0F // 0000 1111 31 mask4 = 0x07 // 0000 0111 32 33 rune1Max = 1<<7 - 1 34 rune2Max = 1<<11 - 1 35 rune3Max = 1<<16 - 1 36 37 // The default lowest and highest continuation byte. 38 locb = 0x80 // 1000 0000 39 hicb = 0xBF // 1011 1111 40 ) 41 42 // decoderune returns the non-ASCII rune at the start of 43 // s[k:] and the index after the rune in s. 44 // 45 // decoderune assumes that caller has checked that 46 // the to be decoded rune is a non-ASCII rune. 47 // 48 // If the string appears to be incomplete or decoding problems 49 // are encountered (runeerror, k + 1) is returned to ensure 50 // progress when decoderune is used to iterate over a string. 51 func decoderune(s string, k int) (r rune, pos int) { 52 pos = k 53 54 if k >= len(s) { 55 return runeError, k + 1 56 } 57 58 s = s[k:] 59 60 switch { 61 case t2 <= s[0] && s[0] < t3: 62 // 0080-07FF two byte sequence 63 if len(s) > 1 && (locb <= s[1] && s[1] <= hicb) { 64 r = rune(s[0]&mask2)<<6 | rune(s[1]&maskx) 65 pos += 2 66 if rune1Max < r { 67 return 68 } 69 } 70 case t3 <= s[0] && s[0] < t4: 71 // 0800-FFFF three byte sequence 72 if len(s) > 2 && (locb <= s[1] && s[1] <= hicb) && (locb <= s[2] && s[2] <= hicb) { 73 r = rune(s[0]&mask3)<<12 | rune(s[1]&maskx)<<6 | rune(s[2]&maskx) 74 pos += 3 75 if rune2Max < r && !(surrogateMin <= r && r <= surrogateMax) { 76 return 77 } 78 } 79 case t4 <= s[0] && s[0] < t5: 80 // 10000-1FFFFF four byte sequence 81 if len(s) > 3 && (locb <= s[1] && s[1] <= hicb) && (locb <= s[2] && s[2] <= hicb) && (locb <= s[3] && s[3] <= hicb) { 82 r = rune(s[0]&mask4)<<18 | rune(s[1]&maskx)<<12 | rune(s[2]&maskx)<<6 | rune(s[3]&maskx) 83 pos += 4 84 if rune3Max < r && r <= maxRune { 85 return 86 } 87 } 88 } 89 90 return runeError, k + 1 91 } 92 93 // encoderune writes into p (which must be large enough) the UTF-8 encoding of the rune. 94 // It returns the number of bytes written. 95 func encoderune(p []byte, r rune) int { 96 // Negative values are erroneous. Making it unsigned addresses the problem. 97 switch i := uint32(r); { 98 case i <= rune1Max: 99 p[0] = byte(r) 100 return 1 101 case i <= rune2Max: 102 _ = p[1] // eliminate bounds checks 103 p[0] = t2 | byte(r>>6) 104 p[1] = tx | byte(r)&maskx 105 return 2 106 case i > maxRune, surrogateMin <= i && i <= surrogateMax: 107 r = runeError 108 fallthrough 109 case i <= rune3Max: 110 _ = p[2] // eliminate bounds checks 111 p[0] = t3 | byte(r>>12) 112 p[1] = tx | byte(r>>6)&maskx 113 p[2] = tx | byte(r)&maskx 114 return 3 115 default: 116 _ = p[3] // eliminate bounds checks 117 p[0] = t4 | byte(r>>18) 118 p[1] = tx | byte(r>>12)&maskx 119 p[2] = tx | byte(r>>6)&maskx 120 p[3] = tx | byte(r)&maskx 121 return 4 122 } 123 } 124
