Related to Issue 205, but not the direct issue: read both copies of the format info...

[zxing.git] / core / src / com / google / zxing / qrcode / decoder / FormatInformation.java

diff --git a/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java b/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
index 2234746..1b76b0d 100644 (file)
--- a/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
+++ b/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2007 Google Inc.
+ * 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.
@@ -16,13 +16,11 @@
 
 package com.google.zxing.qrcode.decoder;
 
-import com.google.zxing.ReaderException;
-
 /**
  * <p>Encapsulates a QR Code's format information, including the data mask used and
  * error correction level.</p>
  *
- * @author srowen@google.com (Sean Owen)
+ * @author Sean Owen
  * @see DataMask
  * @see ErrorCorrectionLevel
  */
@@ -33,7 +31,7 @@ final class FormatInformation {
   /**
    * See ISO 18004:2006, Annex C, Table C.1
    */
-  private static final int[][] FORMAT_INFO_DECODE_LOOKUP = new int[][]{
+  private static final int[][] FORMAT_INFO_DECODE_LOOKUP = {
       {0x5412, 0x00},
       {0x5125, 0x01},
       {0x5E7C, 0x02},
@@ -72,12 +70,12 @@ final class FormatInformation {
    * Offset i holds the number of 1 bits in the binary representation of i
    */
   private static final int[] BITS_SET_IN_HALF_BYTE =
-      new int[]{0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2, 3, 2, 3, 3, 4};
+      {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) throws ReaderException {
+  private FormatInformation(int formatInfo) {
     // Bits 3,4
     errorCorrectionLevel = ErrorCorrectionLevel.forBits((formatInfo >> 3) & 0x03);
     // Bottom 3 bits
@@ -98,39 +96,51 @@ final class FormatInformation {
   }
 
   /**
-   * @param rawFormatInfo
-   * @return
+   * @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 rawFormatInfo) throws ReaderException {
-    FormatInformation formatInfo = doDecodeFormatInformation(rawFormatInfo);
+  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, 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(maskedFormatInfo1 ^ FORMAT_INFO_MASK_QR,
+                                     maskedFormatInfo2 ^ FORMAT_INFO_MASK_QR);
   }
 
-  private static FormatInformation doDecodeFormatInformation(int rawFormatInfo) throws ReaderException {
-    // Unmask:
-    int unmaskedFormatInfo = rawFormatInfo ^ 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 == unmaskedFormatInfo) {
+      if (targetInfo == maskedFormatInfo1 || targetInfo == maskedFormatInfo2) {
         // Found an exact match
         return new FormatInformation(decodeInfo[1]);
       }
-      int bitsDifference = numBitsDiffering(unmaskedFormatInfo, targetInfo);
+      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);
     }