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添加项目文件。
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akwkevin
262
zxing.core/xx/common/StringUtils.cs
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262
zxing.core/xx/common/StringUtils.cs
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/*
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* Copyright (C) 2010 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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using System;
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using System.Collections.Generic;
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using System.Text;
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namespace ZXing.Common
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{
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/// <summary>
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/// Common string-related functions.
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/// </summary>
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/// <author>Sean Owen</author>
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/// <author>Alex Dupre</author>
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public static class StringUtils
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{
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private const String PLATFORM_DEFAULT_ENCODING = "UTF-8";
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public static String SHIFT_JIS = "SJIS";
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public static String GB2312 = "GB2312";
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private const String EUC_JP = "EUC-JP";
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private const String UTF8 = "UTF-8";
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private const String ISO88591 = "ISO-8859-1";
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private static readonly bool ASSUME_SHIFT_JIS =
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String.Compare(SHIFT_JIS, PLATFORM_DEFAULT_ENCODING, StringComparison.OrdinalIgnoreCase) == 0 ||
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String.Compare(EUC_JP, PLATFORM_DEFAULT_ENCODING, StringComparison.OrdinalIgnoreCase) == 0;
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/// <summary>
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/// Guesses the encoding.
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/// </summary>
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/// <param name="bytes">bytes encoding a string, whose encoding should be guessed</param>
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/// <param name="hints">decode hints if applicable</param>
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/// <returns>name of guessed encoding; at the moment will only guess one of:
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/// {@link #SHIFT_JIS}, {@link #UTF8}, {@link #ISO88591}, or the platform
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/// default encoding if none of these can possibly be correct</returns>
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public static String guessEncoding(byte[] bytes, IDictionary<DecodeHintType, object> hints)
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{
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if (hints != null && hints.ContainsKey(DecodeHintType.CHARACTER_SET))
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{
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String characterSet = (String)hints[DecodeHintType.CHARACTER_SET];
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if (characterSet != null)
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{
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return characterSet;
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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 = true;
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bool canBeShiftJIS = true;
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bool canBeUTF8 = true;
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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 = bytes.Length > 3 &&
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bytes[0] == 0xEF &&
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bytes[1] == 0xBB &&
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bytes[2] == 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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{
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int value = bytes[i] & 0xFF;
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// UTF-8 stuff
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if (canBeUTF8)
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{
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if (utf8BytesLeft > 0)
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{
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if ((value & 0x80) == 0)
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{
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canBeUTF8 = false;
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}
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else
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{
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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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{
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if ((value & 0x40) == 0)
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{
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canBeUTF8 = false;
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}
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else
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{
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utf8BytesLeft++;
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if ((value & 0x20) == 0)
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{
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utf2BytesChars++;
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}
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else
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{
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utf8BytesLeft++;
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if ((value & 0x10) == 0)
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{
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utf3BytesChars++;
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}
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else
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{
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utf8BytesLeft++;
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if ((value & 0x08) == 0)
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{
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utf4BytesChars++;
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}
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else
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{
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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 (canBeISO88591)
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{
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if (value > 0x7F && value < 0xA0)
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{
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canBeISO88591 = false;
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}
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else if (value > 0x9F)
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{
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if (value < 0xC0 || value == 0xD7 || value == 0xF7)
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{
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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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{
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if (sjisBytesLeft > 0)
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{
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if (value < 0x40 || value == 0x7F || value > 0xFC)
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{
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canBeShiftJIS = false;
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}
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else
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{
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sjisBytesLeft--;
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}
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}
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else if (value == 0x80 || value == 0xA0 || value > 0xEF)
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{
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canBeShiftJIS = false;
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}
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else if (value > 0xA0 && value < 0xE0)
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{
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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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{
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sjisMaxKatakanaWordLength = sjisCurKatakanaWordLength;
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}
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}
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else if (value > 0x7F)
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{
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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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{
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sjisMaxDoubleBytesWordLength = sjisCurDoubleBytesWordLength;
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}
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}
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else
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{
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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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{
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canBeUTF8 = false;
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}
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if (canBeShiftJIS && sjisBytesLeft > 0)
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{
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canBeShiftJIS = false;
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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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{
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return UTF8;
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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 && (ASSUME_SHIFT_JIS || sjisMaxKatakanaWordLength >= 3 || sjisMaxDoubleBytesWordLength >= 3))
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{
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return SHIFT_JIS;
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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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{
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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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{
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return ISO88591;
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}
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if (canBeShiftJIS)
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{
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return SHIFT_JIS;
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}
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if (canBeUTF8)
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{
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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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}
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}
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