Faster getNextSet; more gains from getNextUnset

git-svn-id: https://zxing.googlecode.com/svn/trunk@2051 59b500cc-1b3d-0410-9834-0bbf25fbcc57

core/src/com/google/zxing/common/BitArray.java

@@ -81,27 +81,46 @@ public final class BitArray {
   /**
    * @param from first bit to check
    * @return index of first bit that is set, starting from the given index, or size if none are set
+   *  at or beyond this given index
+   * @see #getNextUnset(int)
    */
   public int getNextSet(int from) {
-    int size = this.size;
     if (from >= size) {
       return size;
     }
     int bitsOffset = from >> 5;
     int currentBits = bits[bitsOffset];
-    int mask = 1 << (from & 0x1F);
-    while ((currentBits & mask) == 0) {
-      if (++from >= size) {
-        break;
-      }
-      if (mask == 0x80000000) {
-        mask = 1;
-        currentBits = bits[++bitsOffset];
-      } else {
-        mask <<= 1;
+    // mask off lesser bits first
+    currentBits &= ~((1 << (from & 0x1F)) - 1);
+    while (currentBits == 0) {
+      if (++bitsOffset == bits.length) {
+        return size;
       }
+      currentBits = bits[bitsOffset];
     }
-    return from;
+    int result = (bitsOffset << 5) + Integer.numberOfTrailingZeros(currentBits);
+    return result > size ? size : result;
+  }
+
+  /**
+   * @see #getNextSet(int)
+   */
+  public int getNextUnset(int from) {
+    if (from >= size) {
+      return size;
+    }
+    int bitsOffset = from >> 5;
+    int currentBits = ~bits[bitsOffset];
+    // mask off lesser bits first
+    currentBits &= ~((1 << (from & 0x1F)) - 1);
+    while (currentBits == 0) {
+      if (++bitsOffset == bits.length) {
+        return size;
+      }
+      currentBits = ~bits[bitsOffset];
+    }
+    int result = (bitsOffset << 5) + Integer.numberOfTrailingZeros(currentBits);
+    return result > size ? size : result;
   }
 
   /**

core/src/com/google/zxing/oned/Code128Reader.java

@@ -413,12 +413,10 @@ public final class Code128Reader extends OneDReader {
     // Check for ample whitespace following pattern, but, to do this we first need to remember that
     // we fudged decoding CODE_STOP since it actually has 7 bars, not 6. There is a black bar left
     // to read off. Would be slightly better to properly read. Here we just skip it:
-    int width = row.getSize();
-    while (nextStart < width && row.get(nextStart)) {
-      nextStart++;
-    }
-    if (!row.isRange(nextStart, Math.min(width, nextStart + (nextStart - lastStart) / 2),
-        false)) {
+    nextStart = row.getNextUnset(nextStart);
+    if (!row.isRange(nextStart,
+                     Math.min(row.getSize(), nextStart + (nextStart - lastStart) / 2),
+                     false)) {
       throw NotFoundException.getNotFoundInstance();
     }
 

core/src/com/google/zxing/oned/UPCEANExtensionSupport.java

@@ -86,9 +86,7 @@ final class UPCEANExtensionSupport {
       if (x != 4) {
         // Read off separator if not last
         rowOffset = row.getNextSet(rowOffset);
-        while (rowOffset < end && row.get(rowOffset)) {
-          rowOffset++;
-        }
+        rowOffset = row.getNextUnset(rowOffset);
       }
     }
 

core/src/com/google/zxing/oned/UPCEANReader.java

@@ -277,15 +277,8 @@ public abstract class UPCEANReader extends OneDReader {
                                 int[] counters) throws NotFoundException {
     int patternLength = pattern.length;
     int width = row.getSize();
-    boolean isWhite = false;
-    while (rowOffset < width) {
-      isWhite = !row.get(rowOffset);
-      if (whiteFirst == isWhite) {
-        break;
-      }
-      rowOffset++;
-    }
-
+    boolean isWhite = whiteFirst;
+    rowOffset = whiteFirst ? row.getNextUnset(rowOffset) : row.getNextSet(rowOffset);
     int counterPosition = 0;
     int patternStart = rowOffset;
     for (int x = rowOffset; x < width; x++) {

core/src/com/google/zxing/oned/rss/expanded/RSSExpandedReader.java

@@ -190,18 +190,14 @@ public final class RSSExpandedReader extends AbstractRSSReader {
   }
 
   private static int getNextSecondBar(BitArray row, int initialPos){
-    int currentPos = initialPos;
-    boolean current = row.get(currentPos);
-
-    while(currentPos < row.getSize() && row.get(currentPos) == current) {
-      currentPos++;
+    int currentPos;
+    if (row.get(initialPos)) {
+      currentPos = row.getNextUnset(initialPos);
+      currentPos = row.getNextSet(currentPos);
+    } else {
+      currentPos = row.getNextSet(initialPos);
+      currentPos = row.getNextUnset(currentPos);
     }
-
-    current = !current;
-    while(currentPos < row.getSize() && row.get(currentPos) == current) {
-      currentPos++;
-    }
-
     return currentPos;
   }
 
@@ -237,7 +233,6 @@ public final class RSSExpandedReader extends AbstractRSSReader {
         throw nfe;
       }
     }
-
     return new ExpandedPair(leftChar, rightChar, pattern, mayBeLast);
   }
 
@@ -374,10 +369,7 @@ public final class RSSExpandedReader extends AbstractRSSReader {
 
       start = this.startEnd[0];
 
-      int firstElementStart = this.startEnd[1] + 1;
-      while (firstElementStart < row.getSize() && row.get(firstElementStart)) {
-        firstElementStart++;
-      }
+      int firstElementStart = row.getNextUnset(this.startEnd[1] + 1);
 
       end = firstElementStart;
       firstCounter = end - this.startEnd[1];

core/test/src/com/google/zxing/common/BitArrayTestCase.java

@@ -19,6 +19,9 @@ package com.google.zxing.common;
 import org.junit.Assert;
 import org.junit.Test;
 
+import java.security.SecureRandom;
+import java.util.Random;
+
 /**
  * @author Sean Owen
  */
@@ -35,30 +38,93 @@ public final class BitArrayTestCase extends Assert {
   }
 
   @Test
-  public void testGetNextSet() {
+  public void testGetNextSet1() {
     BitArray array = new BitArray(32);
-    assertEquals(32, array.getNextSet(0));
-    assertEquals(32, array.getNextSet(31));
-
+    for (int i = 0; i < array.getSize(); i++) {
+      assertEquals(String.valueOf(i), 32, array.getNextSet(i));
+    }
     array = new BitArray(33);
-    assertEquals(33, array.getNextSet(0));
-    assertEquals(33, array.getNextSet(31));
-    assertEquals(33, array.getNextSet(32));
+    for (int i = 0; i < array.getSize(); i++) {
+      assertEquals(String.valueOf(i), 33, array.getNextSet(i));
+    }
+  }
   
+  @Test
+  public void testGetNextSet2() {
+    BitArray array = new BitArray(33);    
     array.set(31);
-    assertEquals(31, array.getNextSet(0));
-    assertEquals(31, array.getNextSet(30));
-    assertEquals(31, array.getNextSet(31));
-    assertEquals(33, array.getNextSet(32));
-
+    for (int i = 0; i < array.getSize(); i++) {
+      assertEquals(String.valueOf(i), i <= 31 ? 31 : 33, array.getNextSet(i));
+    }
     array = new BitArray(33);
     array.set(32);
-    assertEquals(32, array.getNextSet(0));
-    assertEquals(32, array.getNextSet(30));
-    assertEquals(32, array.getNextSet(31));
-    assertEquals(32, array.getNextSet(32));
+    for (int i = 0; i < array.getSize(); i++) {
+      assertEquals(String.valueOf(i), 32, array.getNextSet(i));
+    }
   }
   
+  @Test
+  public void testGetNextSet3() {
+    BitArray array = new BitArray(63);    
+    array.set(31);
+    array.set(32);
+    for (int i = 0; i < array.getSize(); i++) {
+      int expected;
+      if (i <= 31) {
+        expected = 31;
+      } else if (i == 32) {
+        expected = 32;
+      } else {
+        expected = 63;
+      }
+      assertEquals(String.valueOf(i), expected, array.getNextSet(i));
+    }
+  }
+
+  @Test
+  public void testGetNextSet4() {
+    BitArray array = new BitArray(63);
+    array.set(33);
+    array.set(40);
+    for (int i = 0; i < array.getSize(); i++) {
+      int expected;
+      if (i <= 33) {
+        expected = 33;
+      } else if (i <= 40) {
+        expected = 40;
+      } else {
+        expected = 63;
+      }
+      assertEquals(String.valueOf(i), expected, array.getNextSet(i));
+    }
+  }
+  
+  @Test
+  public void testGetNextSet5() {
+    Random r = new SecureRandom(new byte[] {(byte) 0xDE, (byte) 0xAD, (byte) 0xBE, (byte) 0xEF});
+    for (int i = 0; i < 10; i++) {
+      BitArray array = new BitArray(1 + r.nextInt(100));
+      int numSet = r.nextInt(20);
+      for (int j = 0; j < numSet; j++) {
+        array.set(r.nextInt(array.getSize()));
+      }
+      int numQueries = r.nextInt(20);
+      for (int j = 0; j < numQueries; j++) {
+        int query = r.nextInt(array.getSize());
+        int expected = query;
+        while (expected < array.getSize() && !array.get(expected)) {
+          expected++;
+        }
+        int actual = array.getNextSet(query);
+        if (actual != expected) {
+          array.getNextSet(query);
+        }
+        assertEquals(expected, actual);
+      }
+    }
+  }
+
+
   @Test
   public void testSetBulk() {
     BitArray array = new BitArray(64);