2 * Copyright 2007 ZXing authors
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
17 package com.google.zxing.qrcode.decoder;
20 * <p>Encapsulates a QR Code's format information, including the data mask used and
21 * error correction level.</p>
25 * @see ErrorCorrectionLevel
27 final class FormatInformation {
29 private static final int FORMAT_INFO_MASK_QR = 0x5412;
32 * See ISO 18004:2006, Annex C, Table C.1
34 private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
70 * Offset i holds the number of 1 bits in the binary representation of i
72 private static final int[] BITS_SET_IN_HALF_BYTE =
73 {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
75 private final ErrorCorrectionLevel errorCorrectionLevel;
76 private final byte dataMask;
78 private FormatInformation(int formatInfo) {
80 errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
82 dataMask = (byte) (formatInfo & 0x07);
85 static int numBitsDiffering(int a, int b) {
86 a ^= b; // a now has a 1 bit exactly where its bit differs with b's
87 // Count bits set quickly with a series of lookups:
88 return BITS_SET_IN_HALF_BYTE[a & 0x0F] +
89 BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)] +
90 BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)] +
91 BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)] +
92 BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)] +
93 BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)] +
94 BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)] +
95 BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)];
99 * @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
105 static FormatInformation decodeFormatInformation(int maskedFormatInfo1, int maskedFormatInfo2) {
106 FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo1, maskedFormatInfo2);
107 if (formatInfo != null) {
110 // Should return null, but, some QR codes apparently
111 // do not mask this info. Try again by actually masking the pattern
113 return doDecodeFormatInformation(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR,
114 maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
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]);
128 int bitsDifference = numBitsDiffering(maskedFormatInfo1, targetInfo);
129 if (bitsDifference < bestDifference) {
130 bestFormatInfo = decodeInfo[1];
131 bestDifference = bitsDifference;
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;
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);
150 ErrorCorrectionLevel getErrorCorrectionLevel() {
151 return errorCorrectionLevel;
158 public int hashCode() {
159 return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
162 public boolean equals(Object o) {
163 if (!(o instanceof FormatInformation)) {
166 FormatInformation other = (FormatInformation) o;
167 return this.errorCorrectionLevel == other.errorCorrectionLevel &&
168 this.dataMask == other.dataMask;