From 84f12a0fbe85d05dc6d2c67ae937633e9fe36609 Mon Sep 17 00:00:00 2001
From: James Ahlborn <jtahlborn@yahoo.com>
Date: Thu, 10 Nov 2011 03:33:02 +0000
Subject: [PATCH] Fix problem with reading row from table with deleted/added
 columns. (fixes 3435774)

git-svn-id: https://svn.code.sf.net/p/jackcess/code/jackcess/trunk@591 f203690c-595d-4dc9-a70b-905162fa7fd2
---
 src/changes/changes.xml                       |  3 +++
 .../jackcess/NullMask.java                    | 25 +++++++++++++------
 2 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/src/changes/changes.xml b/src/changes/changes.xml
index a2a9ae6..df41751 100644
--- a/src/changes/changes.xml
+++ b/src/changes/changes.xml
@@ -13,6 +13,9 @@
         Fix problem with creating tables with indexes where ms access could
         not open the created table.
       </action>
+      <action dev="jahlborn" type="fix" issue="3435774">
+        Fix problem with reading row from table with deleted/added columns.
+      </action>
     </release>
     <release version="1.2.5" date="2011-10-19">
       <action dev="jahlborn" type="update">
diff --git a/src/java/com/healthmarketscience/jackcess/NullMask.java b/src/java/com/healthmarketscience/jackcess/NullMask.java
index dd5d959..5be5218 100644
--- a/src/java/com/healthmarketscience/jackcess/NullMask.java
+++ b/src/java/com/healthmarketscience/jackcess/NullMask.java
@@ -36,18 +36,21 @@ import java.nio.ByteBuffer;
  */
 public class NullMask {
   
+  /** num row columns */
+  private final int _columnCount;
   /** The actual bitmask */
-  private byte[] _mask;
+  private final byte[] _mask;
   
   /**
    * @param columnCount Number of columns in the row that this mask will be
    *    used for
    */
   public NullMask(int columnCount) {
+    _columnCount = columnCount;
     // we leave everything initially marked as null so that we don't need to
     // do anything for deleted columns (we only need to mark as non-null
     // valid columns for which we actually have values).
-    _mask = new byte[(columnCount + 7) / 8];
+    _mask = new byte[(_columnCount + 7) / 8];
   }
   
   /**
@@ -72,14 +75,13 @@ public class NullMask {
    */
   public boolean isNull(Column column) {
     int columnNumber = column.getColumnNumber();
-    int maskIndex = columnNumber / 8;
     // if new columns were added to the table, old null masks may not include
     // them (meaning the field is null)
-    if(maskIndex >= _mask.length) {
+    if(columnNumber >= _columnCount) {
       // it's null
       return true;
     }
-    return (_mask[maskIndex] & (byte) (1 << (columnNumber % 8))) == 0;
+    return (_mask[byteIndex(columnNumber)] & bitMask(columnNumber)) == 0;
   }
 
   /**
@@ -89,8 +91,8 @@ public class NullMask {
    */
   public void markNotNull(Column column) {
     int columnNumber = column.getColumnNumber();
-    int maskIndex = columnNumber / 8;
-    _mask[maskIndex] = (byte) (_mask[maskIndex] | (byte) (1 << (columnNumber % 8)));
+    int maskIndex = byteIndex(columnNumber);
+    _mask[maskIndex] = (byte) (_mask[maskIndex] | bitMask(columnNumber));
   }
   
   /**
@@ -99,5 +101,12 @@ public class NullMask {
   public int byteSize() {
     return _mask.length;
   }
-  
+
+  private static int byteIndex(int columnNumber) {
+    return columnNumber / 8;
+  }
+
+  private static byte bitMask(int columnNumber) {
+    return (byte) (1 << (columnNumber % 8));
+  }
 }
-- 
2.39.5