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C++ port of r2157
git-svn-id: https://zxing.googlecode.com/svn/trunk@2202 59b500cc-1b3d-0410-9834-0bbf25fbcc57
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smparkes@smparkes.net
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e57ed43976
commit
8fde7556cf
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@ -35,34 +35,40 @@ char const* const StringUtils::ISO88591 = "ISO8859-1";
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const bool StringUtils::ASSUME_SHIFT_JIS = false;
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string
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StringUtils::guessEncoding(unsigned char* bytes, int length, Hashtable const& hints) {
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StringUtils::guessEncoding(unsigned char* bytes, int length,
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Hashtable const& hints) {
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Hashtable::const_iterator i = hints.find(DecodeHints::CHARACTER_SET);
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if (i != hints.end()) {
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return i->second;
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}
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// Does it start with the UTF-8 byte order mark? then guess it's UTF-8
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if (length > 3 &&
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bytes[0] == (unsigned char) 0xEF &&
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bytes[1] == (unsigned char) 0xBB &&
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bytes[2] == (unsigned char) 0xBF) {
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return UTF8;
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}
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typedef bool boolean;
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// For now, merely tries to distinguish ISO-8859-1, UTF-8 and Shift_JIS,
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// which should be by far the most common encodings. ISO-8859-1
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// should not have bytes in the 0x80 - 0x9F range, while Shift_JIS
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// uses this as a first byte of a two-byte character. If we see this
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// followed by a valid second byte in Shift_JIS, assume it is Shift_JIS.
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// If we see something else in that second byte, we'll make the risky guess
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// that it's UTF-8.
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bool canBeISO88591 = true;
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bool canBeShiftJIS = true;
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bool canBeUTF8 = true;
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// which should be by far the most common encodings.
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boolean canBeISO88591 = true;
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boolean canBeShiftJIS = true;
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boolean canBeUTF8 = true;
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int utf8BytesLeft = 0;
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int maybeDoubleByteCount = 0;
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int maybeSingleByteKatakanaCount = 0;
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bool sawLatin1Supplement = false;
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bool sawUTF8Start = false;
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bool lastWasPossibleDoubleByteStart = false;
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//int utf8LowChars = 0;
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int utf2BytesChars = 0;
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int utf3BytesChars = 0;
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int utf4BytesChars = 0;
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int sjisBytesLeft = 0;
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//int sjisLowChars = 0;
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int sjisKatakanaChars = 0;
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//int sjisDoubleBytesChars = 0;
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int sjisCurKatakanaWordLength = 0;
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int sjisCurDoubleBytesWordLength = 0;
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int sjisMaxKatakanaWordLength = 0;
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int sjisMaxDoubleBytesWordLength = 0;
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//int isoLowChars = 0;
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//int isoHighChars = 0;
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int isoHighOther = 0;
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typedef unsigned char byte;
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boolean utf8bom = length > 3 &&
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bytes[0] == (byte) 0xEF &&
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bytes[1] == (byte) 0xBB &&
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bytes[2] == (byte) 0xBF;
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for (int i = 0;
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i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
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@ -71,105 +77,122 @@ StringUtils::guessEncoding(unsigned char* bytes, int length, Hashtable const& hi
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int value = bytes[i] & 0xFF;
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// UTF-8 stuff
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if (value >= 0x80 && value <= 0xBF) {
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if (canBeUTF8) {
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if (utf8BytesLeft > 0) {
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utf8BytesLeft--;
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}
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} else {
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if (utf8BytesLeft > 0) {
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canBeUTF8 = false;
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}
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if (value >= 0xC0 && value <= 0xFD) {
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sawUTF8Start = true;
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int valueCopy = value;
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while ((valueCopy & 0x40) != 0) {
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utf8BytesLeft++;
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valueCopy <<= 1;
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if ((value & 0x80) == 0) {
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canBeUTF8 = false;
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} else {
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utf8BytesLeft--;
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}
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}
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} else if ((value & 0x80) != 0) {
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if ((value & 0x40) == 0) {
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canBeUTF8 = false;
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} else {
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utf8BytesLeft++;
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if ((value & 0x20) == 0) {
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utf2BytesChars++;
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} else {
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utf8BytesLeft++;
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if ((value & 0x10) == 0) {
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utf3BytesChars++;
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} else {
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utf8BytesLeft++;
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if ((value & 0x08) == 0) {
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utf4BytesChars++;
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} else {
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canBeUTF8 = false;
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}
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}
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}
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}
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} //else {
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//utf8LowChars++;
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//}
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}
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// ISO-8859-1 stuff
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if ((value == 0xC2 || value == 0xC3) && i < length - 1) {
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// This is really a poor hack. The slightly more exotic characters people might want to put in
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// a QR Code, by which I mean the Latin-1 supplement characters (e.g. u-umlaut) have encodings
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// that start with 0xC2 followed by [0xA0,0xBF], or start with 0xC3 followed by [0x80,0xBF].
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int nextValue = bytes[i + 1] & 0xFF;
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if (nextValue <= 0xBF &&
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((value == 0xC2 && nextValue >= 0xA0) || (value == 0xC3 && nextValue >= 0x80))) {
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sawLatin1Supplement = true;
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}
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}
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if (value >= 0x7F && value <= 0x9F) {
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canBeISO88591 = false;
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if (canBeISO88591) {
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if (value > 0x7F && value < 0xA0) {
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canBeISO88591 = false;
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} else if (value > 0x9F) {
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if (value < 0xC0 || value == 0xD7 || value == 0xF7) {
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isoHighOther++;
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} //else {
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//isoHighChars++;
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//}
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} //else {
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//isoLowChars++;
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//}
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}
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// Shift_JIS stuff
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if (value >= 0xA1 && value <= 0xDF) {
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// count the number of characters that might be a Shift_JIS single-byte Katakana character
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if (!lastWasPossibleDoubleByteStart) {
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maybeSingleByteKatakanaCount++;
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}
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}
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if (!lastWasPossibleDoubleByteStart &&
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((value >= 0xF0 && value <= 0xFF) || value == 0x80 || value == 0xA0)) {
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canBeShiftJIS = false;
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}
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if ((value >= 0x81 && value <= 0x9F) || (value >= 0xE0 && value <= 0xEF)) {
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// These start double-byte characters in Shift_JIS. Let's see if it's followed by a valid
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// second byte.
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if (lastWasPossibleDoubleByteStart) {
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// If we just checked this and the last byte for being a valid double-byte
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// char, don't check starting on this byte. If this and the last byte
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// formed a valid pair, then this shouldn't be checked to see if it starts
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// a double byte pair of course.
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lastWasPossibleDoubleByteStart = false;
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} else {
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// ... otherwise do check to see if this plus the next byte form a valid
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// double byte pair encoding a character.
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lastWasPossibleDoubleByteStart = true;
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if (i >= length - 1) {
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if (canBeShiftJIS) {
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if (sjisBytesLeft > 0) {
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if (value < 0x40 || value == 0x7F || value > 0xFC) {
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canBeShiftJIS = false;
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} else {
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int nextValue = bytes[i + 1] & 0xFF;
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if (nextValue < 0x40 || nextValue > 0xFC) {
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canBeShiftJIS = false;
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} else {
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maybeDoubleByteCount++;
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}
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// There is some conflicting information out there about which bytes can follow which in
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// double-byte Shift_JIS characters. The rule above seems to be the one that matches practice.
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sjisBytesLeft--;
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}
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} else if (value == 0x80 || value == 0xA0 || value > 0xEF) {
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canBeShiftJIS = false;
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} else if (value > 0xA0 && value < 0xE0) {
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sjisKatakanaChars++;
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sjisCurDoubleBytesWordLength = 0;
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sjisCurKatakanaWordLength++;
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if (sjisCurKatakanaWordLength > sjisMaxKatakanaWordLength) {
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sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
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}
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} else if (value > 0x7F) {
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sjisBytesLeft++;
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//sjisDoubleBytesChars++;
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sjisCurKatakanaWordLength = 0;
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sjisCurDoubleBytesWordLength++;
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if (sjisCurDoubleBytesWordLength > sjisMaxDoubleBytesWordLength) {
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sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
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}
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} else {
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//sjisLowChars++;
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sjisCurKatakanaWordLength = 0;
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sjisCurDoubleBytesWordLength = 0;
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}
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} else {
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lastWasPossibleDoubleByteStart = false;
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}
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}
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if (utf8BytesLeft > 0) {
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if (canBeUTF8 && utf8BytesLeft > 0) {
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canBeUTF8 = false;
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}
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// Easy -- if assuming Shift_JIS and no evidence it can't be, done
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if (canBeShiftJIS && ASSUME_SHIFT_JIS) {
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return SHIFT_JIS;
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if (canBeShiftJIS && sjisBytesLeft > 0) {
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canBeShiftJIS = false;
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}
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if (canBeUTF8 && sawUTF8Start) {
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// Easy -- if there is BOM or at least 1 valid not-single byte character (and no evidence it can't be UTF-8), done
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if (canBeUTF8 && (utf8bom || utf2BytesChars + utf3BytesChars + utf4BytesChars > 0)) {
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return UTF8;
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}
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// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough. The crude heuristic is:
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// - If we saw
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// - at least 3 bytes that starts a double-byte value (bytes that are rare in ISO-8859-1), or
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// - over 5% of bytes could be single-byte Katakana (also rare in ISO-8859-1),
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// - and, saw no sequences that are invalid in Shift_JIS, then we conclude Shift_JIS
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if (canBeShiftJIS && (maybeDoubleByteCount >= 3 || 20 * maybeSingleByteKatakanaCount > length)) {
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// Easy -- if assuming Shift_JIS or at least 3 valid consecutive not-ascii characters (and no evidence it can't be), done
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if (canBeShiftJIS && (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
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return SHIFT_JIS;
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}
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// Otherwise, we default to ISO-8859-1 unless we know it can't be
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if (!sawLatin1Supplement && canBeISO88591) {
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// Distinguishing Shift_JIS and ISO-8859-1 can be a little tough for short words. The crude heuristic is:
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// - If we saw
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// - only two consecutive katakana chars in the whole text, or
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// - at least 10% of bytes that could be "upper" not-alphanumeric Latin1,
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// - then we conclude Shift_JIS, else ISO-8859-1
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if (canBeISO88591 && canBeShiftJIS) {
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return (sjisMaxKatakanaWordLength == 2 && sjisKatakanaChars == 2) || isoHighOther * 10 >= length
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? SHIFT_JIS : ISO88591;
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}
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// Otherwise, try in order ISO-8859-1, Shift JIS, UTF-8 and fall back to default platform encoding
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if (canBeISO88591) {
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return ISO88591;
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}
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if (canBeShiftJIS) {
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return SHIFT_JIS;
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}
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if (canBeUTF8) {
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return UTF8;
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}
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// Otherwise, we take a wild guess with platform encoding
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return PLATFORM_DEFAULT_ENCODING;
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}
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