bits.java

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/**
 * @(#)Bits.java	1.14 03/01/23
 *
 * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 */
package com.sun.tools.javac.v8.util;

/**
 * A class for extensible, mutable bit sets.
 */
public class Bits {
    private static final int wordlen = 32;
    private static final int wordshift = 5;
    private static final int wordmask = wordlen - 1;
    private int[] bits;

    /**
     * Construct an initially empty set.
     */
    public Bits() {
        this(new int[1]);
    }

    /**
      * Construct a set consisting initially of given bit vector.
      */
    public Bits(int[] bits) {
        super();
        this.bits = bits;
    }

    /**
      * Construct a set consisting initially of given range.
      */
    public Bits(int start, int limit) {
        this();
        inclRange(start, limit);
    }

    private void sizeTo(int len) {
        if (bits.length < len) {
            int[] newbits = new int[len];
            System.arraycopy(bits, 0, newbits, 0, bits.length);
            bits = newbits;
        }
    }

    /**
      * This set = {}.
      */
    public void clear() {
        for (int i = 0; i < bits.length; i++)
            bits[i] = 0;
    }

    /**
      * Return a copy of this set.
      */
    public Bits dup() {
        int[] newbits = new int[bits.length];
        System.arraycopy(bits, 0, newbits, 0, bits.length);
        return new Bits(newbits);
    }

    /**
      * Include x in this set.
      */
    public void incl(int x) {
        assert x >= 0;
        sizeTo((x >>> wordshift) + 1);
        bits[x >>> wordshift] = bits[x >>> wordshift] | (1 << (x & wordmask));
    }

    /**
      * Include [start..limit) in this set.
      */
    public void inclRange(int start, int limit) {
        sizeTo((limit >>> wordshift) + 1);
        for (int x = start; x < limit; x++)
            bits[x >>> wordshift] = bits[x >>> wordshift] | (1 << (x & wordmask));
    }

    /**
      * Exclude x from this set.
      */
    public void excl(int x) {
        assert x >= 0;
        sizeTo((x >>> wordshift) + 1);
        bits[x >>> wordshift] = bits[x >>> wordshift] & ~(1 << (x & wordmask));
    }

    /**
      * Is x an element of this set?
      */
    public boolean isMember(int x) {
        return 0 <= x && x < (bits.length << wordshift) &&
                (bits[x >>> wordshift] & (1 << (x & wordmask))) != 0;
    }

    /**
      * this set = this set & xs.
      */
    public Bits andSet(Bits xs) {
        sizeTo(xs.bits.length);
        for (int i = 0; i < xs.bits.length; i++)
            bits[i] = bits[i] & xs.bits[i];
        return this;
    }

    /**
      * this set = this set | xs.
      */
    public Bits orSet(Bits xs) {
        sizeTo(xs.bits.length);
        for (int i = 0; i < xs.bits.length; i++)
            bits[i] = bits[i] | xs.bits[i];
        return this;
    }

    /**
      * this set = this set \ xs.
      */
    public Bits diffSet(Bits xs) {
        for (int i = 0; i < bits.length; i++) {
            if (i < xs.bits.length) {
                bits[i] = bits[i] & ~xs.bits[i];
            }
        }
        return this;
    }

    /**
      * this set = this set ^ xs.
      */
    public Bits xorSet(Bits xs) {
        sizeTo(xs.bits.length);
        for (int i = 0; i < xs.bits.length; i++)
            bits[i] = bits[i] ^ xs.bits[i];
        return this;
    }

    /**
      * Count trailing zero bits in an int. Algorithm from "Hacker's
      *  Delight" by Henry S. Warren Jr. (figure 5-13)
      */
    private static int trailingZeroBits(int x) {
        assert wordlen == 32;
        if (x == 0)
            return 32;
        int n = 1;
        if ((x & 65535) == 0) {
            n += 16;
            x >>>= 16;
        }
        if ((x & 255) == 0) {
            n += 8;
            x >>>= 8;
        }
        if ((x & 15) == 0) {
            n += 4;
            x >>>= 4;
        }
        if ((x & 3) == 0) {
            n += 2;
            x >>>= 2;
        }
        return n - (x & 1);
    }

    /**
      * Return the index of the least bit position >= x that is set.
      *  If none are set, returns -1.  This provides a nice way to iterate
      *  over the members of a bit set:
      *  <pre>
      *  for (int i = bits.nextBit(0); i>=0; i = bits.nextBit(i+1)) ...
      *  </pre>
      */
    public int nextBit(int x) {
        int windex = x >>> wordshift;
        if (windex >= bits.length)
            return -1;
        int word = bits[windex] & ~((1 << (x & wordmask)) - 1);
        while (true) {
            if (word != 0)
                return (windex << wordshift) + trailingZeroBits(word);
            windex++;
            if (windex >= bits.length)
                return -1;
            word = bits[windex];
        }
    }

    /**
      * a string representation of this set.
      */
    public String toString() {
        char[] digits = new char[bits.length * wordlen];
        for (int i = 0; i < bits.length * wordlen; i++)
            digits[i] = isMember(i) ? '1' : '0';
        return new String(digits);
    }

    /**
      * Test Bits.nextBit(int).
      */
    public static void main(String[] args) {
        java.util.Random r = new java.util.Random();
        Bits bits = new Bits();
        int dupCount = 0;
        for (int i = 0; i < 125; i++) {
            int k;
            do {
                k = r.nextInt(250);
            } while (bits.isMember(k))
                ;
            System.out.println("adding " + k);
            bits.incl(k);
        }
        int count = 0;
        for (int i = bits.nextBit(0); i >= 0; i = bits.nextBit(i + 1)) {
            System.out.println("found " + i);
            count++;
        }
        if (count != 125)
            throw new Error();
    }
}