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 
~CharsetRecog_UTF8()19 CharsetRecog_UTF8::~CharsetRecog_UTF8()
20 {
21     // nothing to do
22 }
23 
getName() const24 const char *CharsetRecog_UTF8::getName() const
25 {
26     return "UTF-8";
27 }
28 
match(InputText * input,CharsetMatch * results) const29 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