/*

 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

 * This code is free software; you can redistribute it and/or modify it

 * under the terms of the GNU General Public License version 2 only, as

 * published by the Free Software Foundation.  Oracle designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Oracle in the LICENSE file that accompanied this code.

 *

 * This code 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

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

 * You should have received a copy of the GNU General Public License version

 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

 *

 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

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 */

package com.sun.tools.javac.util;

import java.util.Arrays;

/** A class for extensible, mutable bit sets.

 *

 *  <p><b>This is NOT part of any supported API.

 *  If you write code that depends on this, you do so at your own risk.

 *  This code and its internal interfaces are subject to change or

 *  deletion without notice.</b>

 */

public class Bits {

    //       ____________      reset    _________

    //      /  UNKNOWN   \   <-------- / UNINIT  \

    //      \____________/       |     \_________/

    //            |              |          |

    //            |assign        |          | any

    //            |        ___________      |

    //            ------> /  NORMAL   \ <----

    //                    \___________/     |

    //                            |         |

    //                            |         |

    //                            -----------

    //                               any

    protected enum BitsState {

        /*  A Bits instance is in UNKNOWN state if it has been explicitly reset.

         *  It is possible to get to this state from any other by calling the

         *  reset method. An instance in the UNKNOWN state can pass to the

         *  NORMAL state after being assigned another Bits instance.

         *

         *  Bits instances are final fields in Flow so the UNKNOWN state models

         *  the null assignment.

         */

        UNKNOWN,

        /*  A Bits instance is in UNINIT when it is created with the default

         *  constructor but it isn't explicitly reset. The main objective of this

         *  internal state is to save some memory.

         */

        UNINIT,

        /*  The normal state is reached after creating a Bits instance from an

         *  existing one or after applying any operation to an instance on UNINIT

         *  or NORMAL state. From this state a bits instance can pass to the

         *  UNKNOWN state by calling the reset method.

         */

        NORMAL;

        static BitsState getState(int[] someBits, boolean reset) {

            if (reset) {

                return UNKNOWN;

            } else {

                if (someBits != unassignedBits) {

                    return NORMAL;

                } else {

                    return UNINIT;

                }

            }

        }

    }

    private final static int wordlen = 32;

    private final static int wordshift = 5;

    private final static int wordmask = wordlen - 1;

    public int[] bits = null;

    // This field will store last version of bits after every change.

    private static final int[] unassignedBits = new int[0];

    protected BitsState currentState;

    /** Construct an initially empty set.

     */

    public Bits() {

        this(false);

    }

    public Bits(Bits someBits) {

        this(someBits.dup().bits, BitsState.getState(someBits.bits, false));

    }

    public Bits(boolean reset) {

        this(unassignedBits, BitsState.getState(unassignedBits, reset));

    }

    /** Construct a set consisting initially of given bit vector.

     */

    protected Bits(int[] bits, BitsState initState) {

        this.bits = bits;

        this.currentState = initState;

        switch (initState) {

            case UNKNOWN:

                this.bits = null;

                break;

            case NORMAL:

                Assert.check(bits != unassignedBits);

                break;

        }

    }

    protected void sizeTo(int len) {

        if (bits.length < len) {

            bits = Arrays.copyOf(bits, len);

        }

    }

    /** This set = {}.

     */

    public void clear() {

        Assert.check(currentState != BitsState.UNKNOWN);

        for (int i = 0; i < bits.length; i++) {

            bits[i] = 0;

        }

        currentState = BitsState.NORMAL;

    }

    public void reset() {

        internalReset();

    }

    protected void internalReset() {

        bits = null;

        currentState = BitsState.UNKNOWN;

    }

    public boolean isReset() {

        return currentState == BitsState.UNKNOWN;

    }

    public Bits assign(Bits someBits) {

        bits = someBits.dup().bits;

        currentState = BitsState.NORMAL;

        return this;

    }

    /** Return a copy of this set.

     */

    public Bits dup() {

        Assert.check(currentState != BitsState.UNKNOWN);

        Bits tmp = new Bits();

        tmp.bits = dupBits();

        currentState = BitsState.NORMAL;

        return tmp;

    }

    protected int[] dupBits() {

        int [] result;

        if (currentState != BitsState.NORMAL) {

            result = bits;

        } else {

            result = new int[bits.length];

            System.arraycopy(bits, 0, result, 0, bits.length);

        }

        return result;

    }

    /** Include x in this set.

     */

    public void incl(int x) {

        Assert.check(currentState != BitsState.UNKNOWN);

        Assert.check(x >= 0);

        sizeTo((x >>> wordshift) + 1);

        bits[x >>> wordshift] = bits[x >>> wordshift] |

            (1 << (x & wordmask));

        currentState = BitsState.NORMAL;

    }

    /** Include [start..limit) in this set.

     */

    public void inclRange(int start, int limit) {

        Assert.check(currentState != BitsState.UNKNOWN);

        sizeTo((limit >>> wordshift) + 1);

        for (int x = start; x < limit; x++) {

            bits[x >>> wordshift] = bits[x >>> wordshift] |

                (1 << (x & wordmask));

        }

        currentState = BitsState.NORMAL;

    }

    /** Exclude [start...end] from this set.

     */

    public void excludeFrom(int start) {

        Assert.check(currentState != BitsState.UNKNOWN);

        Bits temp = new Bits();

        temp.sizeTo(bits.length);

        temp.inclRange(0, start);

        internalAndSet(temp);

        currentState = BitsState.NORMAL;

    }

    /** Exclude x from this set.

     */

    public void excl(int x) {

        Assert.check(currentState != BitsState.UNKNOWN);

        Assert.check(x >= 0);

        sizeTo((x >>> wordshift) + 1);

        bits[x >>> wordshift] = bits[x >>> wordshift] &

            ~(1 << (x & wordmask));

        currentState = BitsState.NORMAL;

    }

    /** Is x an element of this set?

     */

    public boolean isMember(int x) {

        Assert.check(currentState != BitsState.UNKNOWN);

        return

            0 <= x && x < (bits.length << wordshift) &&

            (bits[x >>> wordshift] & (1 << (x & wordmask))) != 0;

    }

    /** {@literal this set = this set & xs}.

     */

    public Bits andSet(Bits xs) {

        Assert.check(currentState != BitsState.UNKNOWN);

        internalAndSet(xs);

        currentState = BitsState.NORMAL;

        return this;

    }

    protected void internalAndSet(Bits xs) {

        Assert.check(currentState != BitsState.UNKNOWN);

        sizeTo(xs.bits.length);

        for (int i = 0; i < xs.bits.length; i++) {

            bits[i] = bits[i] & xs.bits[i];

        }

    }

    /** this set = this set | xs.

     */

    public Bits orSet(Bits xs) {

        Assert.check(currentState != BitsState.UNKNOWN);

        sizeTo(xs.bits.length);

        for (int i = 0; i < xs.bits.length; i++) {

            bits[i] = bits[i] | xs.bits[i];

        }

        currentState = BitsState.NORMAL;

        return this;

    }

    /** this set = this set \ xs.

     */

    public Bits diffSet(Bits xs) {

        Assert.check(currentState != BitsState.UNKNOWN);

        for (int i = 0; i < bits.length; i++) {

            if (i < xs.bits.length) {

                bits[i] = bits[i] & ~xs.bits[i];

            }

        }

        currentState = BitsState.NORMAL;

        return this;

    }

    /** this set = this set ^ xs.

     */

    public Bits xorSet(Bits xs) {

        Assert.check(currentState != BitsState.UNKNOWN);

        sizeTo(xs.bits.length);

        for (int i = 0; i < xs.bits.length; i++) {

            bits[i] = bits[i] ^ xs.bits[i];

        }

        currentState = BitsState.NORMAL;

        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.check(wordlen == 32);

        if (x == 0) {

            return 32;

        }

        int n = 1;

        if ((x & 0xffff) == 0) { n += 16; x >>>= 16; }

        if ((x & 0x00ff) == 0) { n +=  8; x >>>=  8; }

        if ((x & 0x000f) == 0) { n +=  4; x >>>=  4; }

        if ((x & 0x0003) == 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>{@code

     *  for (int i = bits.nextBit(0); i>=0; i = bits.nextBit(i+1)) ...

     *  }</pre>

     */

    public int nextBit(int x) {

        Assert.check(currentState != BitsState.UNKNOWN);

        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.

     */

    @Override

    public String toString() {

        if (bits != null && bits.length > 0) {

            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);

        } else {

            return "[]";

        }

    }

}