Author: kahatlen
Date: Fri Jan 26 00:15:00 2007
New Revision: 500177
URL: http://svn.apache.org/viewvc?view=rev&rev=500177
Log:
DERBY-2191: Cleanup of FormatableBitSet
Use unsigned int operations to calculate positions.
Patch contributed by Dyre Tjeldvoll.
Modified:
db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/io/FormatableBitSet.java
db/derby/code/trunk/java/testing/org/apache/derbyTesting/unitTests/junit/FormatableBitSetTest.java
Modified: db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/io/FormatableBitSet.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/io/FormatableBitSet.java?view=diff&rev=500177&r1=500176&r2=500177
==============================================================================
--- db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/io/FormatableBitSet.java (original)
+++ db/derby/code/trunk/java/engine/org/apache/derby/iapi/services/io/FormatableBitSet.java Fri Jan 26 00:15:00 2007
@@ -70,11 +70,11 @@
// value is never null. An empty bitset is represented by a
// zero-length array.
private byte[] value;
- private short bitsInLastByte;
+ private byte bitsInLastByte;
private transient int lengthAsBits;
- private void checkPosition(int p) {
+ private final void checkPosition(int p) {
if (p < 0 || lengthAsBits <= p) {
throw new
IllegalArgumentException("Bit position "+p+
@@ -82,6 +82,18 @@
}
}
+ // Division, multiplication and remainder calcuation of a positive
+ // number with a power of two can be done using shifts and bit
+ // masking. The compiler attempts this optimization but since Java
+ // does not have unsigned ints it will also have to create code to
+ // handle negative values. In this class the argument is
+ // frequently an array index or array length, which is known not
+ // to be negative. These utility methods allow us to perform
+ // "unsigned" operations with 8. Hopefully the extra function call
+ // will be inlined by the compiler.
+ private static int udiv8(int i) { return (i>>3); }
+ private static byte umod8(int i) { return (byte)(i&0x7); }
+
/**
* Niladic Constructor
*/
@@ -95,6 +107,11 @@
*/
public FormatableBitSet(int numBits)
{
+ if (numBits < 0) {
+ throw new
+ IllegalArgumentException("Bit set size "+ numBits +
+ " is not allowed");
+ }
initializeBits(numBits);
}
@@ -324,6 +341,11 @@
*/
public FormatableBitSet shrink(int n)
{
+ if (n < 0) {
+ throw new
+ IllegalArgumentException("Bit set size "+ n +
+ " is not allowed");
+ }
int numBytes;
int lastByteNum;
@@ -494,13 +516,12 @@
public final boolean isSet(int position)
{
checkPosition(position);
-
- int bytepos = position / 8;
- int bitpos = 7 - (position % 8);
-
- return ((value[bytepos] & (1 << bitpos)) != 0);
+ final int byteIndex = udiv8(position);
+ final byte bitIndex = umod8(position);
+ return ((value[byteIndex] & (0x80>>bitIndex)) != 0);
}
+
/**
* Bit get -- alias for isSet()
*
@@ -521,11 +542,9 @@
public void set(int position)
{
checkPosition(position);
-
- int bytepos = position / 8;
- int bitpos = 7 - (position % 8);
-
- value[bytepos] |= (1 << bitpos);
+ final int byteIndex = udiv8(position);
+ final byte bitIndex = umod8(position);
+ value[byteIndex] |= (0x80>>bitIndex);
}
/**
@@ -537,11 +556,9 @@
public void clear(int position)
{
checkPosition(position);
-
- int bytepos = position / 8;
- int bitpos = 7 - (position % 8);
-
- value[bytepos] &= ~(1 << bitpos);
+ final int byteIndex = udiv8(position);
+ final byte bitIndex = umod8(position);
+ value[byteIndex] &= ~(0x80>>bitIndex);
}
/**
@@ -575,13 +592,12 @@
*
* @return the number of bits
*/
- private static short
+ private static byte
numBitsInLastByte(int bits)
{
- int modulo = bits % 8;
- return (short)((modulo == 0) ?
- ((bits == 0) ? 0 : 8) :
- modulo);
+ if (bits == 0) return 0;
+ byte lastbits = umod8(bits);
+ return (lastbits != 0 ? lastbits : 8);
}
/**
Modified: db/derby/code/trunk/java/testing/org/apache/derbyTesting/unitTests/junit/FormatableBitSetTest.java
URL: http://svn.apache.org/viewvc/db/derby/code/trunk/java/testing/org/apache/derbyTesting/unitTests/junit/FormatableBitSetTest.java?view=diff&rev=500177&r1=500176&r2=500177
==============================================================================
--- db/derby/code/trunk/java/testing/org/apache/derbyTesting/unitTests/junit/FormatableBitSetTest.java (original)
+++ db/derby/code/trunk/java/testing/org/apache/derbyTesting/unitTests/junit/FormatableBitSetTest.java Fri Jan 26 00:15:00 2007
@@ -152,13 +152,8 @@
assertTrue(nineBits.invariantHolds());
}
public void testIntCtorNeg() {
- // Should throw an exception?
- FormatableBitSet negBits = new FormatableBitSet(-1);
- assertEquals(-1,negBits.getLength());
- assertEquals(0,negBits.getLengthInBytes());
- assertEquals(0,negBits.getByteArray().length);
- assertEquals(0,negBits.getNumBitsSet());
- assertTrue(negBits.invariantHolds());
+ try { FormatableBitSet negBits = new FormatableBitSet(-1); fail(); }
+ catch(IllegalArgumentException iae) {}
}
// Test cases for the copy constructor
@@ -239,7 +234,7 @@
try {
bitset18.shrink(-9);
fail();
- } catch (ArrayIndexOutOfBoundsException e) {}
+ } catch (IllegalArgumentException iae) {}
}
// Should be allowed?
public void testShrink0() {