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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;
/**
* <p>Encapsulates a QR Code's format information, including the data mask used and
* error correction level.</p>
*
* @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},
};
/**
* Offset i holds the number of 1 bits in the binary representation of i
*/
private static final int[] BITS_SET_IN_HALF_BYTE =
{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
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) {
a ^= b; // a now has a 1 bit exactly where its bit differs with b's
// Count bits set quickly with a series of lookups:
return BITS_SET_IN_HALF_BYTE[a & 0x0F] +
BITS_SET_IN_HALF_BYTE[(a >>> 4 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 8 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 12 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 16 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 20 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 24 & 0x0F)] +
BITS_SET_IN_HALF_BYTE[(a >>> 28 & 0x0F)];
}
/**
* @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</code>
* 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 i = 0; i < FORMAT_INFO_DECODE_LOOKUP.length; i++) {
int[] decodeInfo = FORMAT_INFO_DECODE_LOOKUP[i];
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;
}
public int hashCode() {
return (errorCorrectionLevel.ordinal() << 3) | (int) dataMask;
}
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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