1 /* 2 ********************************************************************** 3 * Copyright (C) 2005-2006, International Business Machines 4 * Corporation and others. All Rights Reserved. 5 ********************************************************************** 6 */ 7 8 #include "unicode/utypes.h" 9 10 #if !UCONFIG_NO_CONVERSION 11 12 #include "csrutf8.h" 13 14 U_NAMESPACE_BEGIN 15 ~CharsetRecog_UTF8()16CharsetRecog_UTF8::~CharsetRecog_UTF8() 17 { 18 // nothing to do 19 } 20 getName() const21const char *CharsetRecog_UTF8::getName() const 22 { 23 return "UTF-8"; 24 } 25 match(InputText * det)26int32_t CharsetRecog_UTF8::match(InputText* det) { 27 bool hasBOM = FALSE; 28 int32_t numValid = 0; 29 int32_t numInvalid = 0; 30 const uint8_t *input = det->fRawInput; 31 int32_t i; 32 int32_t trailBytes = 0; 33 int32_t confidence; 34 35 if (det->fRawLength >= 3 && 36 input[0] == 0xEF && input[1] == 0xBB && input[2] == 0xBF) { 37 hasBOM = TRUE; 38 } 39 40 // Scan for multi-byte sequences 41 for (i=0; i < det->fRawLength; i += 1) { 42 int32_t b = input[i]; 43 44 if ((b & 0x80) == 0) { 45 continue; // ASCII 46 } 47 48 // Hi bit on char found. Figure out how long the sequence should be 49 if ((b & 0x0E0) == 0x0C0) { 50 trailBytes = 1; 51 } else if ((b & 0x0F0) == 0x0E0) { 52 trailBytes = 2; 53 } else if ((b & 0x0F8) == 0xF0) { 54 trailBytes = 3; 55 } else { 56 numInvalid += 1; 57 58 if (numInvalid > 5) { 59 break; 60 } 61 62 trailBytes = 0; 63 } 64 65 // Verify that we've got the right number of trail bytes in the sequence 66 for (;;) { 67 i += 1; 68 69 if (i >= det->fRawLength) { 70 break; 71 } 72 73 b = input[i]; 74 75 if ((b & 0xC0) != 0x080) { 76 numInvalid += 1; 77 break; 78 } 79 80 if (--trailBytes == 0) { 81 numValid += 1; 82 break; 83 } 84 } 85 86 } 87 88 // Cook up some sort of confidence score, based on presense of a BOM 89 // and the existence of valid and/or invalid multi-byte sequences. 90 confidence = 0; 91 if (hasBOM && numInvalid == 0) { 92 confidence = 100; 93 } else if (hasBOM && numValid > numInvalid*10) { 94 confidence = 80; 95 } else if (numValid > 3 && numInvalid == 0) { 96 confidence = 100; 97 } else if (numValid > 0 && numInvalid == 0) { 98 confidence = 80; 99 } else if (numValid == 0 && numInvalid == 0) { 100 // Plain ASCII. 101 confidence = 10; 102 } else if (numValid > numInvalid*10) { 103 // Probably corruput utf-8 data. Valid sequences aren't likely by chance. 104 confidence = 25; 105 } 106 107 return confidence; 108 } 109 110 U_NAMESPACE_END 111 #endif 112