001/* 002 * Copyright 2007 ZXing authors 003 * 004 * Licensed under the Apache License, Version 2.0 (the "License"); 005 * you may not use this file except in compliance with the License. 006 * You may obtain a copy of the License at 007 * 008 * http://www.apache.org/licenses/LICENSE-2.0 009 * 010 * Unless required by applicable law or agreed to in writing, software 011 * distributed under the License is distributed on an "AS IS" BASIS, 012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 013 * See the License for the specific language governing permissions and 014 * limitations under the License. 015 */ 016 017package com.itextpdf.text.pdf.qrcode; 018 019/** 020 * <p>Encapsulates a QR Code's format information, including the data mask used and 021 * error correction level.</p> 022 * 023 * @author Sean Owen 024 * @see ErrorCorrectionLevel 025 * @since 5.0.2 026 */ 027final class FormatInformation { 028 029 private static final int FORMAT_INFO_MASK_QR = 0x5412; 030 031 /** 032 * See ISO 18004:2006, Annex C, Table C.1 033 */ 034 private static final int[][] FORMAT_INFO_DECODE_LOOKUP = { 035 {0x5412, 0x00}, 036 {0x5125, 0x01}, 037 {0x5E7C, 0x02}, 038 {0x5B4B, 0x03}, 039 {0x45F9, 0x04}, 040 {0x40CE, 0x05}, 041 {0x4F97, 0x06}, 042 {0x4AA0, 0x07}, 043 {0x77C4, 0x08}, 044 {0x72F3, 0x09}, 045 {0x7DAA, 0x0A}, 046 {0x789D, 0x0B}, 047 {0x662F, 0x0C}, 048 {0x6318, 0x0D}, 049 {0x6C41, 0x0E}, 050 {0x6976, 0x0F}, 051 {0x1689, 0x10}, 052 {0x13BE, 0x11}, 053 {0x1CE7, 0x12}, 054 {0x19D0, 0x13}, 055 {0x0762, 0x14}, 056 {0x0255, 0x15}, 057 {0x0D0C, 0x16}, 058 {0x083B, 0x17}, 059 {0x355F, 0x18}, 060 {0x3068, 0x19}, 061 {0x3F31, 0x1A}, 062 {0x3A06, 0x1B}, 063 {0x24B4, 0x1C}, 064 {0x2183, 0x1D}, 065 {0x2EDA, 0x1E}, 066 {0x2BED, 0x1F}, 067 }; 068 069 /** 070 * Offset i holds the number of 1 bits in the binary representation of i 071 */ 072 private static final int[] BITS_SET_IN_HALF_BYTE = 073 {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4}; 074 075 private final ErrorCorrectionLevel errorCorrectionLevel; 076 private final byte dataMask; 077 078 private FormatInformation(int formatInfo) { 079 // Bits 3,4 080 errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03); 081 // Bottom 3 bits 082 dataMask = (byte) (formatInfo & 0x07); 083 } 084 085 static int numBitsDiffering(int a, int b) { 086 a ^= b; // a now has a 1 bit exactly where its bit differs with b's 087 // Count bits set quickly with a series of lookups: 088 return BITS_SET_IN_HALF_BYTE[a & 0x0F] + 089 BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)] + 090 BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)] + 091 BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)] + 092 BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)] + 093 BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)] + 094 BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)] + 095 BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)]; 096 } 097 098 /** 099 * @param maskedFormatInfo1 format info indicator, with mask still applied 100 * @param maskedFormatInfo2 second copy of same info; both are checked at the same time 101 * to establish best match 102 * @return information about the format it specifies, or <code>null</code> 103 * if doesn't seem to match any known pattern 104 */ 105 static FormatInformation decodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) { 106 FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo1, maskedFormatInfo2); 107 if (formatInfo != null) { 108 return formatInfo; 109 } 110 // Should return null, but, some QR codes apparently 111 // do not mask this info. Try again by actually masking the pattern 112 // first 113 return doDecodeFormatInformation(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR, 114 maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR); 115 } 116 117 private static FormatInformation doDecodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) { 118 // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing 119 int bestDifference = Integer.MAX_VALUE; 120 int bestFormatInfo = 0; 121 for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) { 122 int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i]; 123 int targetInfo = decodeInfo[0]; 124 if (targetInfo == maskedFormatInfo1 || targetInfo == maskedFormatInfo2) { 125 // Found an exact match 126 return new FormatInformation(decodeInfo[1]); 127 } 128 int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo); 129 if (bitsDifference < bestDifference) { 130 bestFormatInfo = decodeInfo[1]; 131 bestDifference = bitsDifference; 132 } 133 if (maskedFormatInfo1 != maskedFormatInfo2) { 134 // also try the other option 135 bitsDifference = numBitsDiffering(maskedFormatInfo2, targetInfo); 136 if (bitsDifference < bestDifference) { 137 bestFormatInfo = decodeInfo[1]; 138 bestDifference = bitsDifference; 139 } 140 } 141 } 142 // Hamming distance of the 32 masked codes is 7, by construction, so <= 3 bits 143 // differing means we found a match 144 if (bestDifference <= 3) { 145 return new FormatInformation(bestFormatInfo); 146 } 147 return null; 148 } 149 150 ErrorCorrectionLevel getErrorCorrectionLevel() { 151 return errorCorrectionLevel; 152 } 153 154 byte getDataMask() { 155 return dataMask; 156 } 157 158 public int hashCode() { 159 return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask; 160 } 161 162 public boolean equals(Object o) { 163 if (!(o instanceof FormatInformation)) { 164 return false; 165 } 166 FormatInformation other = (FormatInformation) o; 167 return this.errorCorrectionLevel == other.errorCorrectionLevel && 168 this.dataMask == other.dataMask; 169 } 170 171}