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 rawFormatInfo
102 static FormatInformation decodeFormatInformation(int rawFormatInfo) {
103 FormatInformation formatInfo = doDecodeFormatInformation(rawFormatInfo);
104 if (formatInfo != null) {
107 // Should return null, but, some QR codes apparently
108 // do not mask this info. Try again, first masking the raw bits so
109 // the function will unmask
110 return doDecodeFormatInformation(rawFormatInfo ^ FORMAT_INFO_MASK_QR);
113 private static FormatInformation doDecodeFormatInformation(int rawFormatInfo) {
115 int unmaskedFormatInfo = rawFormatInfo ^ FORMAT_INFO_MASK_QR;
116 // Find the int in FORMAT_INFO_DECODE_LOOKUP with fewest bits differing
117 int bestDifference = Integer.MAX_VALUE;
118 int bestFormatInfo = 0;
119 for (int i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) {
120 int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
121 int targetInfo = decodeInfo[0];
122 if (targetInfo == unmaskedFormatInfo) {
123 // Found an exact match
124 return new FormatInformation(decodeInfo[1]);
126 int bitsDifference = numBitsDiffering(unmaskedFormatInfo, targetInfo);
127 if (bitsDifference < bestDifference) {
128 bestFormatInfo = decodeInfo[1];
129 bestDifference = bitsDifference;
132 if (bestDifference <= 3) {
133 return new FormatInformation(bestFormatInfo);
138 ErrorCorrectionLevel getErrorCorrectionLevel() {
139 return errorCorrectionLevel;
146 public int hashCode() {
147 return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
150 public boolean equals(Object o) {
151 if (!(o instanceof FormatInformation)) {
154 FormatInformation other = (FormatInformation) o;
155 return this.errorCorrectionLevel == other.errorCorrectionLevel &&
156 this.dataMask == other.dataMask;