112 lines
3.0 KiB
C++
112 lines
3.0 KiB
C++
// Copyright (C) 2016 and later: Unicode, Inc. and others.
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// License & terms of use: http://www.unicode.org/copyright.html
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/*
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**********************************************************************
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* Copyright (C) 2005-2014, International Business Machines
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* Corporation and others. All Rights Reserved.
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**********************************************************************
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*/
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#include "unicode/utypes.h"
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#if !UCONFIG_NO_CONVERSION
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#include "csrutf8.h"
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#include "csmatch.h"
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U_NAMESPACE_BEGIN
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CharsetRecog_UTF8::~CharsetRecog_UTF8()
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{
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// nothing to do
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}
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const char *CharsetRecog_UTF8::getName() const
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{
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return "UTF-8";
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}
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UBool CharsetRecog_UTF8::match(InputText* input, CharsetMatch *results) const {
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bool hasBOM = FALSE;
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int32_t numValid = 0;
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int32_t numInvalid = 0;
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const uint8_t *inputBytes = input->fRawInput;
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int32_t i;
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int32_t trailBytes = 0;
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int32_t confidence;
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if (input->fRawLength >= 3 &&
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inputBytes[0] == 0xEF && inputBytes[1] == 0xBB && inputBytes[2] == 0xBF) {
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hasBOM = TRUE;
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}
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// Scan for multi-byte sequences
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for (i=0; i < input->fRawLength; i += 1) {
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int32_t b = inputBytes[i];
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if ((b & 0x80) == 0) {
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continue; // ASCII
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}
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// Hi bit on char found. Figure out how long the sequence should be
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if ((b & 0x0E0) == 0x0C0) {
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trailBytes = 1;
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} else if ((b & 0x0F0) == 0x0E0) {
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trailBytes = 2;
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} else if ((b & 0x0F8) == 0xF0) {
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trailBytes = 3;
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} else {
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numInvalid += 1;
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continue;
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}
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// Verify that we've got the right number of trail bytes in the sequence
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for (;;) {
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i += 1;
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if (i >= input->fRawLength) {
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break;
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}
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b = inputBytes[i];
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if ((b & 0xC0) != 0x080) {
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numInvalid += 1;
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break;
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}
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if (--trailBytes == 0) {
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numValid += 1;
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break;
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}
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}
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}
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// Cook up some sort of confidence score, based on presence of a BOM
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// and the existence of valid and/or invalid multi-byte sequences.
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confidence = 0;
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if (hasBOM && numInvalid == 0) {
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confidence = 100;
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} else if (hasBOM && numValid > numInvalid*10) {
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confidence = 80;
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} else if (numValid > 3 && numInvalid == 0) {
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confidence = 100;
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} else if (numValid > 0 && numInvalid == 0) {
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confidence = 80;
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} else if (numValid == 0 && numInvalid == 0) {
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// Plain ASCII. Confidence must be > 10, it's more likely than UTF-16, which
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// accepts ASCII with confidence = 10.
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confidence = 15;
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} else if (numValid > numInvalid*10) {
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// Probably corruput utf-8 data. Valid sequences aren't likely by chance.
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confidence = 25;
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}
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results->set(input, this, confidence);
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return (confidence > 0);
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}
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U_NAMESPACE_END
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#endif
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