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/* Soot - a J*va Optimization Framework
* Copyright (C) 2001 Felix Kwok
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2.1 of the License, or (at your option) any later version.
*
* This library 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
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the
* Free Software Foundation, Inc., 59 Temple Place - Suite 330,
* Boston, MA 02111-1307, USA.
*/
/*
* Modified by the Sable Research Group and others 1997-1999.
* See the 'credits' file distributed with Soot for the complete list of
* contributors. (Soot is distributed at http://www.sable.mcgill.ca/soot)
*/
package soot.util;
import java.util.*;
/** A fast enumerator for sparse bit sets. When the enumerator is
* created, it takes a snapshot of the underlying BitVector, and iterates
* through the set bits. Note that this class almost implements the
* Iterator interface, but it doesn't because the return type of next
* is int rather than Object. */
public class BitSetIterator {
long[] bits; // Bits inherited from the underlying BitVector
int index; // The 64-bit block currently being examined
long save = 0; // A copy of the 64-bit block (for fast access)
/* Computes log_2(x) modulo 67. This uses the fact that 2 is a
* primitive root modulo 67 */
final static int[] lookup = {-1, 0, 1, 39, 2, 15, 40, 23, 3, 12, 16,
59, 41, 19, 24, 54, 4, -1, 13, 10, 17,
62, 60, 28, 42, 30, 20, 51, 25, 44, 55,
47, 5, 32, -1, 38, 14, 22, 11, 58, 18,
53, -1, 9, 61, 27, 29, 50, 43, 46, 31,
37, 21, 57, 52, 8, 26, 49, 45, 36, 56,
7, 48, 35, 6, 34, 33};
/** Creates a new BitSetIterator */
BitSetIterator(long[] bits) {
//this.bits = new long[bits.length];
//System.arraycopy(bits,0,this.bits,0,bits.length);
this.bits = bits;
index = 0;
/* Zip through empty blocks */
while (index < bits.length && bits[index]==0L)
index++;
if (index < bits.length)
save = bits[index];
}
/** Returns true if there are more set bits in the BitVector; false otherwise. */
public boolean hasNext() {
return index < bits.length;
}
/** Returns the index of the next set bit. Note that the return type is int,
* and not Object. */
public int next() {
if (index >= bits.length)
throw new NoSuchElementException();
long k = (save & (save-1)); // Clears the last non-zero bit. save is guaranteed non-zero.
long diff = save ^ k; // Finds out which bit it is. diff has exactly one bit set.
save = k;
// Computes the position of the set bit.
int result = (diff < 0) ? 64 * index + 63 : 64 * index + lookup[(int)(diff%67)];
if (save == 0) {
index++;
while (index < bits.length && bits[index]==0L)
index++;
if (index < bits.length)
save = bits[index];
}
return result;
}
}
