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/*
 * Copyright 2007 ZXing authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.zxing.qrcode.decoder;

/**
 * 

Encapsulates a QR Code's format information, including the data mask used and * error correction level.

* * @author Sean Owen * @see DataMask * @see ErrorCorrectionLevel */ final class FormatInformation { private static final int FORMAT_INFO_MASK_QR = 0x5412; /** * See ISO 18004:2006, Annex C, Table C.1 */ private static final int[][] FORMAT_INFO_DECODE_LOOKUP = { {0x5412, 0x00}, {0x5125, 0x01}, {0x5E7C, 0x02}, {0x5B4B, 0x03}, {0x45F9, 0x04}, {0x40CE, 0x05}, {0x4F97, 0x06}, {0x4AA0, 0x07}, {0x77C4, 0x08}, {0x72F3, 0x09}, {0x7DAA, 0x0A}, {0x789D, 0x0B}, {0x662F, 0x0C}, {0x6318, 0x0D}, {0x6C41, 0x0E}, {0x6976, 0x0F}, {0x1689, 0x10}, {0x13BE, 0x11}, {0x1CE7, 0x12}, {0x19D0, 0x13}, {0x0762, 0x14}, {0x0255, 0x15}, {0x0D0C, 0x16}, {0x083B, 0x17}, {0x355F, 0x18}, {0x3068, 0x19}, {0x3F31, 0x1A}, {0x3A06, 0x1B}, {0x24B4, 0x1C}, {0x2183, 0x1D}, {0x2EDA, 0x1E}, {0x2BED, 0x1F}, }; private final ErrorCorrectionLevel errorCorrectionLevel; private final byte dataMask; private FormatInformation(int formatInfo) { // Bits 3,4 errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03); // Bottom 3 bits dataMask = (byte) (formatInfo & 0x07); } static int numBitsDiffering(int a, int b) { return Integer.bitCount(a ^ b); } /** * @param maskedFormatInfo1 format info indicator, with mask still applied * @param maskedFormatInfo2 second copy of same info; both are checked at the same time * to establish best match * @return information about the format it specifies, or {@code null} * if doesn't seem to match any known pattern */ static FormatInformation decodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) { FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo1, maskedFormatInfo2); if (formatInfo != null) { return formatInfo; } // Should return null, but, some QR codes apparently // do not mask this info. Try again by actually masking the pattern // first return doDecodeFormatInformation(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR, maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR); } private static FormatInformation doDecodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) { // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing int bestDifference = Integer.MAX_VALUE; int bestFormatInfo = 0; for (int[] decodeInfo : FORMAT_INFO_DECODE_LOOKUP) { int targetInfo = decodeInfo[0]; if (targetInfo == maskedFormatInfo1 || targetInfo == maskedFormatInfo2) { // Found an exact match return new FormatInformation(decodeInfo[1]); } int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo); if (bitsDifference < bestDifference) { bestFormatInfo = decodeInfo[1]; bestDifference = bitsDifference; } if (maskedFormatInfo1 != maskedFormatInfo2) { // also try the other option bitsDifference = numBitsDiffering(maskedFormatInfo2, targetInfo); if (bitsDifference < bestDifference) { bestFormatInfo = decodeInfo[1]; bestDifference = bitsDifference; } } } // Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits // differing means we found a match if (bestDifference <= 3) { return new FormatInformation(bestFormatInfo); } return null; } ErrorCorrectionLevel getErrorCorrectionLevel() { return errorCorrectionLevel; } byte getDataMask() { return dataMask; } @Override public int hashCode() { return (errorCorrectionLevel.ordinal() << 3) | dataMask; } @Override public boolean equals(Object o) { if (!(o instanceof FormatInformation)) { return false; } FormatInformation other = (FormatInformation) o; return this.errorCorrectionLevel == other.errorCorrectionLevel && this.dataMask == other.dataMask; } }




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