/*
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* Copyright 2012 ZXing authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#import "ZXByteArray.h"
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#import "ZXDecodeHints.h"
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#import "ZXStringUtils.h"
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@implementation ZXStringUtils
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+ (NSStringEncoding)guessEncoding:(ZXByteArray *)bytes hints:(ZXDecodeHints *)hints {
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NSStringEncoding systemEncoding = CFStringConvertEncodingToNSStringEncoding(CFStringGetSystemEncoding());
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BOOL assumeShiftJIS = systemEncoding == NSShiftJISStringEncoding || systemEncoding == NSJapaneseEUCStringEncoding;
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if (hints != nil) {
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NSStringEncoding encoding = hints.encoding;
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if (encoding > 0) {
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return encoding;
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}
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}
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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.
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int length = bytes.length;
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BOOL canBeISO88591 = YES;
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BOOL canBeShiftJIS = YES;
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BOOL canBeUTF8 = YES;
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int utf8BytesLeft = 0;
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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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BOOL utf8bom = length > 3 &&
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bytes.array[0] == (int8_t) 0xEF &&
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bytes.array[1] == (int8_t) 0xBB &&
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bytes.array[2] == (int8_t) 0xBF;
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for (int i = 0;
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i < length && (canBeISO88591 || canBeShiftJIS || canBeUTF8);
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i++) {
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int value = bytes.array[i] & 0xFF;
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// UTF-8 stuff
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if (canBeUTF8) {
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if (utf8BytesLeft > 0) {
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if ((value & 0x80) == 0) {
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canBeUTF8 = NO;
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} else {
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utf8BytesLeft--;
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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 = NO;
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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 = NO;
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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 (canBeISO88591) {
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if (value > 0x7F && value < 0xA0) {
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canBeISO88591 = NO;
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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 (canBeShiftJIS) {
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if (sjisBytesLeft > 0) {
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if (value < 0x40 || value == 0x7F || value > 0xFC) {
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canBeShiftJIS = NO;
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} else {
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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 = NO;
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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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}
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}
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if (canBeUTF8 && utf8BytesLeft > 0) {
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canBeUTF8 = NO;
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}
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if (canBeShiftJIS && sjisBytesLeft > 0) {
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canBeShiftJIS = NO;
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}
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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 NSUTF8StringEncoding;
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}
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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 && (assumeShiftJIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3)) {
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return NSShiftJISStringEncoding;
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}
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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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? NSShiftJISStringEncoding : NSISOLatin1StringEncoding;
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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 NSISOLatin1StringEncoding;
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}
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if (canBeShiftJIS) {
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return NSShiftJISStringEncoding;
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}
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if (canBeUTF8) {
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return NSUTF8StringEncoding;
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}
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// Otherwise, we take a wild guess with platform encoding
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return systemEncoding;
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}
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@end
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