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Fix for old logic error in seeking format information -- actually was comparing unmasked rather than masked values, though it ended up working

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git-svn-id: https://zxing.googlecode.com/svn/trunk@1052 59b500cc-1b3d-0410-9834-0bbf25fbcc57
This commit is contained in:
srowen 2009-09-14 10:17:17 +00:00
parent 2b0d14963d
commit eef79f730b
2 changed files with 23 additions and 20 deletions
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25
core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
View file

@ -96,39 +96,40 @@ final class FormatInformation {
}
/**
* @param rawFormatInfo
* @return
* @param maskedFormatInfo format info indicator, with mask still applied
* @return information about the format it specifies, or <code>null</code>
* if doesn't seem to match any known pattern
*/
static FormatInformation decodeFormatInformation(int rawFormatInfo) {
FormatInformation formatInfo = doDecodeFormatInformation(rawFormatInfo);
static FormatInformation decodeFormatInformation(int maskedFormatInfo) {
FormatInformation formatInfo = doDecodeFormatInformation(maskedFormatInfo);
if (formatInfo != null) {
return formatInfo;
}
// Should return null, but, some QR codes apparently
// do not mask this info. Try again, first masking the raw bits so
// the function will unmask
return doDecodeFormatInformation(rawFormatInfo ^ FORMAT_INFO_MASK_QR);
// do not mask this info. Try again by actually masking the pattern
// first
return doDecodeFormatInformation(maskedFormatInfo ^ FORMAT_INFO_MASK_QR);
}
private static FormatInformation doDecodeFormatInformation(int rawFormatInfo) {
// Unmask:
int unmaskedFormatInfo = rawFormatInfo ^ FORMAT_INFO_MASK_QR;
private static FormatInformation doDecodeFormatInformation(int maskedFormatInfo) {
// 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 == unmaskedFormatInfo) {
if (targetInfo == maskedFormatInfo) {
// Found an exact match
return new FormatInformation(decodeInfo[1]);
}
int bitsDifference = numBitsDiffering(unmaskedFormatInfo, targetInfo);
int bitsDifference = numBitsDiffering(maskedFormatInfo, 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);
}

18
core/test/src/com/google/zxing/qrcode/decoder/FormatInformationTestCase.java
View file

@ -16,7 +16,6 @@
package com.google.zxing.qrcode.decoder;
import com.google.zxing.ReaderException;
import junit.framework.TestCase;
/**
@ -24,6 +23,9 @@ import junit.framework.TestCase;
*/
public final class FormatInformationTestCase extends TestCase {
private static final int MASKED_TEST_FORMAT_INFO = 0x2BED;
private static final int UNMASKED_TEST_FORMAT_INFO = MASKED_TEST_FORMAT_INFO ^ 0x5412;
public void testBitsDiffering() {
assertEquals(0, FormatInformation.numBitsDiffering(1, 1));
assertEquals(1, FormatInformation.numBitsDiffering(0, 2));
@ -31,19 +33,19 @@ public final class FormatInformationTestCase extends TestCase {
assertEquals(32, FormatInformation.numBitsDiffering(-1, 0));
}
public void testDecode() throws ReaderException {
public void testDecode() {
// Normal case
FormatInformation expected = FormatInformation.decodeFormatInformation(0x2BED ^ 0x5412);
FormatInformation expected = FormatInformation.decodeFormatInformation(MASKED_TEST_FORMAT_INFO);
assertEquals((byte) 0x07, expected.getDataMask());
assertEquals(ErrorCorrectionLevel.Q, expected.getErrorCorrectionLevel());
// where the code forgot the mask!
assertEquals(expected, FormatInformation.decodeFormatInformation(0x2BED));
assertEquals(expected, FormatInformation.decodeFormatInformation(UNMASKED_TEST_FORMAT_INFO));
// 1,2,3,4 bits difference
assertEquals(expected, FormatInformation.decodeFormatInformation(0x2BEF ^ 0x5412));
assertEquals(expected, FormatInformation.decodeFormatInformation(0x2BEE ^ 0x5412));
assertEquals(expected, FormatInformation.decodeFormatInformation(0x2BEA ^ 0x5412));
assertNull(FormatInformation.decodeFormatInformation(0x2BE2 ^ 0x5412));
assertEquals(expected, FormatInformation.decodeFormatInformation(MASKED_TEST_FORMAT_INFO ^ 0x01));
assertEquals(expected, FormatInformation.decodeFormatInformation(MASKED_TEST_FORMAT_INFO ^ 0x03));
assertEquals(expected, FormatInformation.decodeFormatInformation(MASKED_TEST_FORMAT_INFO ^ 0x07));
assertNull(FormatInformation.decodeFormatInformation(MASKED_TEST_FORMAT_INFO ^ 0x0F));
}
}