--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/org/tmatesoft/hg/util/SparseSet.java	Wed Aug 17 02:35:15 2011 +0200
@@ -0,0 +1,227 @@
+/*
+ * Copyright (c) 2011 TMate Software Ltd
+ *  
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * For information on how to redistribute this software under
+ * the terms of a license other than GNU General Public License
+ * contact TMate Software at support@hg4j.com
+ */
+package org.tmatesoft.hg.util;
+
+import org.tmatesoft.hg.internal.Experimental;
+
+/**
+ * WORK IN PROGRESS, DO NOT USE
+ * Memory-friendly alternative to HashMap-backed Pool. Set where object can be obtained (not only queried for presence)
+ * 
+ * cpython repo, use of HashMap Pool results in ~6 Mb of Map.Entry and Map.Entry[],
+ * while use of SparseSet result in 2 Mb. 
+ * 
+ * @author Artem Tikhomirov
+ * @author TMate Software Ltd.
+ */
+@Experimental(reason="Requires tuning to accomodate to collection size. Present state (6-6-6) is too much for a lot of uses")
+public class SparseSet<T> {
+	
+	public static void main(String[] args) {
+		SparseSet<String> ss = new SparseSet<String>();
+		String one = Integer.toString(156), two = Integer.toString(1024), three = Integer.toString(1123123);
+		ss.put(one);
+		ss.put(two);
+		ss.put(three);
+		System.out.println(one == ss.get(one));
+		System.out.println(two == ss.get(two));
+		System.out.println(three == ss.get(three));
+		System.out.println(null == ss.get("one"));
+		System.out.println(one == ss.get(Integer.toString(156)));
+		System.out.println(two == ss.get(Integer.toString(1024)));
+		System.out.println(three == ss.get(Integer.toString(1123123)));
+		ss.dump();
+	}
+
+	private static class IndexBranch {
+		private final LeafBranch[] leafs = new LeafBranch[64];
+	}
+	private static class LeafBranch {
+		private final Object[] data = new Object[64];
+	}
+
+	private final int[] fixups = new int[] {0x1, 0x10, 0xA, 0xD, 0x1F }; // rehash attempts
+	private final IndexBranch[] level2 = new IndexBranch[64];
+	private int size = 0;
+
+	public void put(T o) {
+		int hash = o.hashCode();
+		//
+		// 8 bits per level
+//		int i1 = (hash >>> 24) & 0xFF, i2 = (hash >>> 16) & 0xFF , i3 = (hash >>> 8) & 0xFF, i4 = hash & 0xFF;
+		//
+		// 10, 8, 8 and 6 bits
+//		final int i1 = (hash >>> 22) & 0x3FF, i2 = (hash >>> 14) & 0xFF , i3 = (hash >>> 6) & 0xFF, i4 = hash & 0x3F;
+		//
+		// 8, 6, 6, 6, 6
+		// 10, 6, 6, 6, 4
+		//
+		// 6, 5, 5, 5 = 21 bit
+//		hash = hash ^ (hash >>> 24); // incorporate upper byte we don't use into lower to value it
+//		final int i1 = (hash >>> 18) & 0x3F, i2 = (hash >>> 12) & 0x1F , i3 = (hash >>> 7) & 0x1F, i4 = (hash >>> 2) & 0x1F;
+		// 6, 5, 5
+//		hash = hash ^ (hash >>> 16);
+//		final int i1 = (hash >>> 10) & 0x3F, i2 = (hash >>> 5) & 0x1F , i3 = hash & 0x1F;
+		//
+		// 6, 6, 6
+		final int i1 = (hash >>> 15) & 0x3F, i2 = (hash >>> 6) & 0x3F , i3 = hash & 0x3F;
+		LeafBranch l3 = leafBranchPut(i1, i2);
+		if (l3.data[i3] == null) {
+			l3.data[i3] = o;
+			size++;
+			return;
+		}
+		int neighbour = (i3+1) & 0x3F; 
+		if (l3.data[neighbour] == null) {
+			l3.data[neighbour] = o;
+			size++;
+			return;
+		}
+		int conflictCount = 0;
+		for (int fixup : fixups) {
+//			if (showConflicts) {
+//				System.out.printf("(fixup: 0x%x) ", fixup);
+//			}
+			l3 = leafBranchPut(i1 ^ fixup, i2);
+			conflictCount++;
+			if (l3.data[i3] != null) {
+//				if (showConflicts) {
+//					System.out.printf("i1 failed ");
+//				}
+				l3 = leafBranchPut(i1, i2 ^ fixup);
+				conflictCount++;
+//				if (showConflicts) {
+//					System.out.printf("i2 %s ",  (l3.data[i3] == null) ? "ok" : "failed");
+//				}
+//			} else {
+//				if (showConflicts) {
+//					System.out.printf("i1 ok");
+//				}
+			}
+//			if (showConflicts) {
+//				System.out.println();
+//			}
+			if (l3.data[i3] == null) {
+				l3.data[i3] = o;
+//				System.out.printf("Resolved conflict in %d steps (fixup 0x%X)\n", conflictCount, fixup);
+				size++;
+				return;
+			}
+		}
+		throw new IllegalStateException(String.valueOf(o));
+	}
+	
+	@SuppressWarnings("unchecked")
+	public T get(T o) {
+		int hash = o.hashCode();
+		//hash = hash ^ (hash >>> 16);
+		final int i1 = (hash >>> 15) & 0x3F, i2 = (hash >>> 6) & 0x3F , i3 = hash & 0x3F;
+		//
+		LeafBranch l3 = leafBranchGet(i1, i2);
+		if (l3 == null || l3.data[i3] == null) {
+			return null;
+		}
+		if (o.equals(l3.data[i3])) {
+			return (T) l3.data[i3];
+		}
+		//
+		int neighbour = (i3+1) & 0x3F; 
+		if (o.equals(l3.data[neighbour])) {
+			return (T) l3.data[neighbour];
+		}
+
+		//
+		// resolve conflict
+		for (int fixup : fixups) {
+			Object data = leafValueGet(i1 ^ fixup, i2, i3);
+			if (data == null) {
+				return null;
+			}
+			if (o.equals(data)) {
+				return (T)data;
+			}
+			data = leafValueGet(i1, i2 ^ fixup, i3);
+			if (data == null) {
+				return null;
+			}
+			if (o.equals(data)) {
+				return (T)data;
+			}
+		}
+		dump();
+		throw new IllegalStateException(String.format("[%d,%d,%d] hash: 0x%X, hash2: 0x%X, %s", i1, i2, i3, o.hashCode(), hash, o));
+	}
+
+	public int size() {
+		return size;
+	}
+	private LeafBranch leafBranchPut(int i1, int i2) {
+		IndexBranch l2 = level2[i1];
+		if (l2 == null) {
+			level2[i1] = l2 = new IndexBranch();
+		}
+		LeafBranch l3 = l2.leafs[i2];
+		if (l3 == null) {
+			l2.leafs[i2] = l3 = new LeafBranch();
+		}
+		return l3;
+	}
+
+	private LeafBranch leafBranchGet(int i1, int i2) {
+		IndexBranch l2 = level2[i1];
+		if (l2 == null) {
+			return null;
+		}
+		return l2.leafs[i2];
+	}
+
+	private Object leafValueGet(int i1, int i2, int i3) {
+		IndexBranch l2 = level2[i1];
+		if (l2 == null) {
+			return null;
+		}
+		LeafBranch l3 = l2.leafs[i2];
+		if (l3 == null) {
+			return null;
+		}
+		return l3.data[i3];
+	}
+
+	public void dump() {
+		int count = 0;
+		for (int i = 0; i < level2.length; i++) {
+			IndexBranch l2 = level2[i];
+			if (l2 == null) {
+				continue;
+			}
+			for (int j = 0; j < l2.leafs.length; j++) {
+				LeafBranch l3 = l2.leafs[j];
+				if (l3 == null) {
+					continue;
+				}
+				for (int k = 0; k < l3.data.length; k++) {
+					Object d = l3.data[k];
+					if (d != null) {
+						System.out.printf("[%3d,%3d,%3d] %s\n", i,j,k,d);
+						count++;
+					}
+				}
+			}
+		}
+		System.out.printf("Total: %d elements", count);
+	}
+}