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 f9cbefe..1b76b0d 100644 (file)
--- a/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
+++ b/core/src/com/google/zxing/qrcode/decoder/FormatInformation.java
@@ -16,8 +16,6 @@
 
 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>
@@ -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);
     }