1 // © 2016 and later: Unicode, Inc. and others. 2 // License & terms of use: http://www.unicode.org/copyright.html 3 /* 4 ********************************************************************** 5 * Copyright (C) 2005-2014, International Business Machines 6 * Corporation and others. All Rights Reserved. 7 ********************************************************************** 8 */ 9 10 #include "unicode/utypes.h" 11 12 #if !UCONFIG_NO_CONVERSION 13 14 #include "csrutf8.h" 15 #include "csmatch.h" 16 17 U_NAMESPACE_BEGIN 18 19 CharsetRecog_UTF8::~CharsetRecog_UTF8() 20 { 21 // nothing to do 22 } 23 24 const char *CharsetRecog_UTF8::getName() const 25 { 26 return "UTF-8"; 27 } 28 29 UBool CharsetRecog_UTF8::match(InputText* input, CharsetMatch *results) const { 30 bool hasBOM = FALSE; 31 int32_t numValid = 0; 32 int32_t numInvalid = 0; 33 const uint8_t *inputBytes = input->fRawInput; 34 int32_t i; 35 int32_t trailBytes = 0; 36 int32_t confidence; 37 38 if (input->fRawLength >= 3 && 39 inputBytes[0] == 0xEF && inputBytes[1] == 0xBB && inputBytes[2] == 0xBF) { 40 hasBOM = TRUE; 41 } 42 43 // Scan for multi-byte sequences 44 for (i=0; i < input->fRawLength; i += 1) { 45 int32_t b = inputBytes[i]; 46 47 if ((b & 0x80) == 0) { 48 continue; // ASCII 49 } 50 51 // Hi bit on char found. Figure out how long the sequence should be 52 if ((b & 0x0E0) == 0x0C0) { 53 trailBytes = 1; 54 } else if ((b & 0x0F0) == 0x0E0) { 55 trailBytes = 2; 56 } else if ((b & 0x0F8) == 0xF0) { 57 trailBytes = 3; 58 } else { 59 numInvalid += 1; 60 continue; 61 } 62 63 // Verify that we've got the right number of trail bytes in the sequence 64 for (;;) { 65 i += 1; 66 67 if (i >= input->fRawLength) { 68 break; 69 } 70 71 b = inputBytes[i]; 72 73 if ((b & 0xC0) != 0x080) { 74 numInvalid += 1; 75 break; 76 } 77 78 if (--trailBytes == 0) { 79 numValid += 1; 80 break; 81 } 82 } 83 84 } 85 86 // Cook up some sort of confidence score, based on presence of a BOM 87 // and the existence of valid and/or invalid multi-byte sequences. 88 confidence = 0; 89 if (hasBOM && numInvalid == 0) { 90 confidence = 100; 91 } else if (hasBOM && numValid > numInvalid*10) { 92 confidence = 80; 93 } else if (numValid > 3 && numInvalid == 0) { 94 confidence = 100; 95 } else if (numValid > 0 && numInvalid == 0) { 96 confidence = 80; 97 } else if (numValid == 0 && numInvalid == 0) { 98 // Plain ASCII. Confidence must be > 10, it's more likely than UTF-16, which 99 // accepts ASCII with confidence = 10. 100 confidence = 15; 101 } else if (numValid > numInvalid*10) { 102 // Probably corruput utf-8 data. Valid sequences aren't likely by chance. 103 confidence = 25; 104 } 105 106 results->set(input, this, confidence); 107 return (confidence > 0); 108 } 109 110 U_NAMESPACE_END 111 #endif 112