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;
19 import com.google.zxing.ReaderException;
22 * <p>Encapsulates a QR Code's format information, including the data mask used and
23 * error correction level.</p>
25 * @author srowen@google.com (Sean Owen)
27 * @see ErrorCorrectionLevel
29 final class FormatInformation {
31 private static final int FORMAT_INFO_MASK_QR = 0x5412;
34 * See ISO 18004:2006, Annex C, Table C.1
36 private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
72 * Offset i holds the number of 1 bits in the binary representation of i
74 private static final int[] BITS_SET_IN_HALF_BYTE =
75 new int[]{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
77 private final ErrorCorrectionLevel errorCorrectionLevel;
78 private final byte dataMask;
80 private FormatInformation(int formatInfo) throws ReaderException {
82 errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
84 dataMask = (byte) (formatInfo & 0x07);
87 static int numBitsDiffering(int a, int b) {
88 a ^= b; // a now has a 1 bit exactly where its bit differs with b's
89 // Count bits set quickly with a series of lookups:
90 return BITS_SET_IN_HALF_BYTE[a & 0x0F] +
91 BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)] +
92 BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)] +
93 BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)] +
94 BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)] +
95 BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)] +
96 BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)] +
97 BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)];
101 * @param rawFormatInfo
104 static FormatInformation decodeFormatInformation(int rawFormatInfo) throws ReaderException {
105 FormatInformation formatInfo = doDecodeFormatInformation(rawFormatInfo);
106 if (formatInfo != null) {
109 // Should return null, but, some QR codes apparently
110 // do not mask this info. Try again, first masking the raw bits so
111 // the function will unmask
112 return doDecodeFormatInformation(rawFormatInfo ^ FORMAT_INFO_MASK_QR);
115 private static FormatInformation doDecodeFormatInformation(int rawFormatInfo) throws ReaderException {
117 int unmaskedFormatInfo = rawFormatInfo ^ FORMAT_INFO_MASK_QR;
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 == unmaskedFormatInfo) {
125 // Found an exact match
126 return new FormatInformation(decodeInfo[1]);
128 int bitsDifference = numBitsDiffering(unmaskedFormatInfo, targetInfo);
129 if (bitsDifference < bestDifference) {
130 bestFormatInfo = decodeInfo[1];
131 bestDifference = bitsDifference;
134 if (bestDifference <= 3) {
135 return new FormatInformation(bestFormatInfo);
140 ErrorCorrectionLevel getErrorCorrectionLevel() {
141 return errorCorrectionLevel;
148 public int hashCode() {
149 return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
152 public boolean equals(Object o) {
153 if (!(o instanceof FormatInformation)) {
156 FormatInformation other = (FormatInformation) o;
157 return this.errorCorrectionLevel == other.errorCorrectionLevel &&
158 this.dataMask == other.dataMask;