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ObjectIdSubclassMap: Use & rather than % for hashing 

Bitwise and is faster than integer modulus operations, and since
the table size is always a power of 2, this is simple to use for
index operation.

Change-Id: I83d01e5c74fd9e910c633a98ea6f90b59092ba29
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
This commit is contained in:
Shawn O. Pearce 2011-03-09 14:26:39 -08:00
parent ff6ac0aaef
commit 47c2a3a98d
1 changed files with 13 additions and 4 deletions
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17
org.eclipse.jgit/src/org/eclipse/jgit/lib/ObjectIdSubclassMap.java
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@ -63,19 +63,23 @@
* type of subclass of ObjectId that will be stored in the map.
*/
public class ObjectIdSubclassMap<V extends ObjectId> implements Iterable<V> {
private static final int INITIAL_TABLE_SIZE = 32;
private int size;
private int mask;
private V[] table;
/** Create an empty map. */
public ObjectIdSubclassMap() {
table = createArray(32);
initTable(INITIAL_TABLE_SIZE);
}
/** Remove all entries from this map. */
public void clear() {
size = 0;
table = createArray(32);
initTable(INITIAL_TABLE_SIZE);
}
/**
@ -210,7 +214,7 @@ public void remove() {
}
private final int index(final AnyObjectId id) {
return (id.w1 >>> 1) % table.length;
return id.w1 & mask;
}
private void insert(final V newValue) {
@ -226,7 +230,7 @@ private void grow() {
final V[] oldTable = table;
final int oldSize = table.length;
table = createArray(2 * oldSize);
initTable(oldSize << 1);
for (int i = 0; i < oldSize; i++) {
final V obj = oldTable[i];
if (obj != null)
@ -234,6 +238,11 @@ private void grow() {
}
}
private void initTable(int sz) {
mask = sz - 1;
table = createArray(sz);
}
@SuppressWarnings("unchecked")
private final V[] createArray(final int sz) {
return (V[]) new ObjectId[sz];