/*

 * 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

 * or visit www.oracle.com if you need additional information or have any

 * questions.

 */

/*

 * This file is available under and governed by the GNU General Public

 * License version 2 only, as published by the Free Software Foundation.

 * However, the following notice accompanied the original version of this

 * file:

 *

 * Written by Doug Lea with assistance from members of JCP JSR-166

 * Expert Group and released to the public domain, as explained at

 * http://creativecommons.org/publicdomain/zero/1.0/

 */

package java.util;

import java.util.concurrent.CountedCompleter;

import java.util.concurrent.ForkJoinPool;

import java.util.function.BinaryOperator;

import java.util.function.DoubleBinaryOperator;

import java.util.function.IntBinaryOperator;

import java.util.function.LongBinaryOperator;

/**

 * ForkJoin tasks to perform Arrays.parallelPrefix operations.

 *

 * @author Doug Lea

 * @since 1.8

 */

class ArrayPrefixHelpers {

    private ArrayPrefixHelpers() {} // non-instantiable

    /*

     * Parallel prefix (aka cumulate, scan) task classes

     * are based loosely on Guy Blelloch's original

     * algorithm (http://www.cs.cmu.edu/~scandal/alg/scan.html):

     *  Keep dividing by two to threshold segment size, and then:

     *   Pass 1: Create tree of partial sums for each segment

     *   Pass 2: For each segment, cumulate with offset of left sibling

     *

     * This version improves performance within FJ framework mainly by

     * allowing the second pass of ready left-hand sides to proceed

     * even if some right-hand side first passes are still executing.

     * It also combines first and second pass for leftmost segment,

     * and skips the first pass for rightmost segment (whose result is

     * not needed for second pass).  It similarly manages to avoid

     * requiring that users supply an identity basis for accumulations

     * by tracking those segments/subtasks for which the first

     * existing element is used as base.

     *

     * Managing this relies on ORing some bits in the pendingCount for

     * phases/states: CUMULATE, SUMMED, and FINISHED. CUMULATE is the

     * main phase bit. When false, segments compute only their sum.

     * When true, they cumulate array elements. CUMULATE is set at

     * root at beginning of second pass and then propagated down. But

     * it may also be set earlier for subtrees with lo==0 (the left

     * spine of tree). SUMMED is a one bit join count. For leafs, it

     * is set when summed. For internal nodes, it becomes true when

     * one child is summed.  When the second child finishes summing,

     * we then moves up tree to trigger the cumulate phase. FINISHED

     * is also a one bit join count. For leafs, it is set when

     * cumulated. For internal nodes, it becomes true when one child

     * is cumulated.  When the second child finishes cumulating, it

     * then moves up tree, completing at the root.

     *

     * To better exploit locality and reduce overhead, the compute

     * method loops starting with the current task, moving if possible

     * to one of its subtasks rather than forking.

     *

     * As usual for this sort of utility, there are 4 versions, that

     * are simple copy/paste/adapt variants of each other.  (The

     * double and int versions differ from long version solely by

     * replacing "long" (with case-matching)).

     */

    // see above

    static final int CUMULATE = 1;

    static final int SUMMED   = 2;

    static final int FINISHED = 4;

    /** The smallest subtask array partition size to use as threshold */

    static final int MIN_PARTITION = 16;

    static final class CumulateTask<T> extends CountedCompleter<Void> {

        final T[] array;

        final BinaryOperator<T> function;

        CumulateTask<T> left, right;

        final int lo, hi, origin, fence, threshold;

        /** Root task constructor */

        public CumulateTask(CumulateTask<T> parent,

                            BinaryOperator<T> function,

                            T[] array, int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.lo = this.origin = lo; this.hi = this.fence = hi;

            int p;

            this.threshold =

                (p = (hi - lo) / (ForkJoinPool.getCommonPoolParallelism() << 3))

                <= MIN_PARTITION ? MIN_PARTITION : p;

        }

        /** Subtask constructor */

        CumulateTask(CumulateTask<T> parent, BinaryOperator<T> function,

                     T[] array, int origin, int fence, int threshold,

                     int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.origin = origin; this.fence = fence;

            this.threshold = threshold;

            this.lo = lo; this.hi = hi;

        }

        public final void compute() {

            final BinaryOperator<T> fn;

            final T[] a;

            if ((fn = this.function) == null || (a = this.array) == null)

                throw new NullPointerException();    // hoist checks

            int th = threshold, org = origin, fnc = fence, l, h;

            CumulateTask<T> t = this;

            outer: while ((l = t.lo) >= 0 && (h = t.hi) <= a.length) {

                if (h - l > th) {

                    CumulateTask<T> lt = t.left, rt = t.right, f;

                    if (lt == null) {                // first pass

                        int mid = (l + h) >>> 1;

                        f = rt = t.right =

                            new CumulateTask<T>(t, fn, a, org, fnc, th, mid, h);

                        t = lt = t.left =

                            new CumulateTask<T>(t, fn, a, org, fnc, th, l, mid);

                    }

                    else {                           // possibly refork

                        T pin = t.in;

                        lt.in = pin;

                        f = t = null;

                        if (rt != null) {

                            T lout = lt.out;

                            rt.in = (l == org ? lout :

                                     fn.apply(pin, lout));

                            for (int c;;) {

                                if (((c = rt.getPendingCount()) & CUMULATE) != 0)

                                    break;

                                if (rt.compareAndSetPendingCount(c, c|CUMULATE)){

                                    t = rt;

                                    break;

                                }

                            }

                        }

                        for (int c;;) {

                            if (((c = lt.getPendingCount()) & CUMULATE) != 0)

                                break;

                            if (lt.compareAndSetPendingCount(c, c|CUMULATE)) {

                                if (t != null)

                                    f = t;

                                t = lt;

                                break;

                            }

                        }

                        if (t == null)

                            break;

                    }

                    if (f != null)

                        f.fork();

                }

                else {

                    int state; // Transition to sum, cumulate, or both

                    for (int b;;) {

                        if (((b = t.getPendingCount()) & FINISHED) != 0)

                            break outer;                      // already done

                        state = ((b & CUMULATE) != 0 ? FINISHED :

                                 (l > org) ? SUMMED : (SUMMED|FINISHED));

                        if (t.compareAndSetPendingCount(b, b|state))

                            break;

                    }

                    T sum;

                    if (state != SUMMED) {

                        int first;

                        if (l == org) {                       // leftmost; no in

                            sum = a[org];

                            first = org + 1;

                        }

                        else {

                            sum = t.in;

                            first = l;

                        }

                        for (int i = first; i < h; ++i)       // cumulate

                            a[i] = sum = fn.apply(sum, a[i]);

                    }

                    else if (h < fnc) {                       // skip rightmost

                        sum = a[l];

                        for (int i = l + 1; i < h; ++i)       // sum only

                            sum = fn.apply(sum, a[i]);

                    }

                    else

                        sum = t.in;

                    t.out = sum;

                    for (CumulateTask<T> par;;) {             // propagate

                        @SuppressWarnings("unchecked") CumulateTask<T> partmp

                            = (CumulateTask<T>)t.getCompleter();

                        if ((par = partmp) == null) {

                            if ((state & FINISHED) != 0)      // enable join

                                t.quietlyComplete();

                            break outer;

                        }

                        int b = par.getPendingCount();

                        if ((b & state & FINISHED) != 0)

                            t = par;                          // both done

                        else if ((b & state & SUMMED) != 0) { // both summed

                            int nextState; CumulateTask<T> lt, rt;

                            if ((lt = par.left) != null &&

                                (rt = par.right) != null) {

                                T lout = lt.out;

                                par.out = (rt.hi == fnc ? lout :

                                           fn.apply(lout, rt.out));

                            }

                            int refork = (((b & CUMULATE) == 0 &&

                                           par.lo == org) ? CUMULATE : 0);

                            if ((nextState = b|state|refork) == b ||

                                par.compareAndSetPendingCount(b, nextState)) {

                                state = SUMMED;               // drop finished

                                t = par;

                                if (refork != 0)

                                    par.fork();

                            }

                        }

                        else if (par.compareAndSetPendingCount(b, b|state))

                            break outer;                      // sib not ready

                    }

                }

            }

        }

        @java.io.Serial

        private static final long serialVersionUID = 5293554502939613543L;

    }

    static final class LongCumulateTask extends CountedCompleter<Void> {

        final long[] array;

        final LongBinaryOperator function;

        LongCumulateTask left, right;

        long in, out;

        final int lo, hi, origin, fence, threshold;

        /** Root task constructor */

        public LongCumulateTask(LongCumulateTask parent,

                                LongBinaryOperator function,

                                long[] array, int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.lo = this.origin = lo; this.hi = this.fence = hi;

            int p;

            this.threshold =

                (p = (hi - lo) / (ForkJoinPool.getCommonPoolParallelism() << 3))

                <= MIN_PARTITION ? MIN_PARTITION : p;

        }

        /** Subtask constructor */

        LongCumulateTask(LongCumulateTask parent, LongBinaryOperator function,

                         long[] array, int origin, int fence, int threshold,

                         int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.origin = origin; this.fence = fence;

            this.threshold = threshold;

            this.lo = lo; this.hi = hi;

        }

        public final void compute() {

            final LongBinaryOperator fn;

            final long[] a;

            if ((fn = this.function) == null || (a = this.array) == null)

                throw new NullPointerException();    // hoist checks

            int th = threshold, org = origin, fnc = fence, l, h;

            LongCumulateTask t = this;

            outer: while ((l = t.lo) >= 0 && (h = t.hi) <= a.length) {

                if (h - l > th) {

                    LongCumulateTask lt = t.left, rt = t.right, f;

                    if (lt == null) {                // first pass

                        int mid = (l + h) >>> 1;

                        f = rt = t.right =

                            new LongCumulateTask(t, fn, a, org, fnc, th, mid, h);

                        t = lt = t.left =

                            new LongCumulateTask(t, fn, a, org, fnc, th, l, mid);

                    }

                    else {                           // possibly refork

                        long pin = t.in;

                        lt.in = pin;

                        f = t = null;

                        if (rt != null) {

                            long lout = lt.out;

                            rt.in = (l == org ? lout :

                                     fn.applyAsLong(pin, lout));

                            for (int c;;) {

                                if (((c = rt.getPendingCount()) & CUMULATE) != 0)

                                    break;

                                if (rt.compareAndSetPendingCount(c, c|CUMULATE)){

                                    t = rt;

                                    break;

                                }

                            }

                        }

                        for (int c;;) {

                            if (((c = lt.getPendingCount()) & CUMULATE) != 0)

                                break;

                            if (lt.compareAndSetPendingCount(c, c|CUMULATE)) {

                                if (t != null)

                                    f = t;

                                t = lt;

                                break;

                            }

                        }

                        if (t == null)

                            break;

                    }

                    if (f != null)

                        f.fork();

                }

                else {

                    int state; // Transition to sum, cumulate, or both

                    for (int b;;) {

                        if (((b = t.getPendingCount()) & FINISHED) != 0)

                            break outer;                      // already done

                        state = ((b & CUMULATE) != 0 ? FINISHED :

                                 (l > org) ? SUMMED : (SUMMED|FINISHED));

                        if (t.compareAndSetPendingCount(b, b|state))

                            break;

                    }

                    long sum;

                    if (state != SUMMED) {

                        int first;

                        if (l == org) {                       // leftmost; no in

                            sum = a[org];

                            first = org + 1;

                        }

                        else {

                            sum = t.in;

                            first = l;

                        }

                        for (int i = first; i < h; ++i)       // cumulate

                            a[i] = sum = fn.applyAsLong(sum, a[i]);

                    }

                    else if (h < fnc) {                       // skip rightmost

                        sum = a[l];

                        for (int i = l + 1; i < h; ++i)       // sum only

                            sum = fn.applyAsLong(sum, a[i]);

                    }

                    else

                        sum = t.in;

                    t.out = sum;

                    for (LongCumulateTask par;;) {            // propagate

                        if ((par = (LongCumulateTask)t.getCompleter()) == null) {

                            if ((state & FINISHED) != 0)      // enable join

                                t.quietlyComplete();

                            break outer;

                        }

                        int b = par.getPendingCount();

                        if ((b & state & FINISHED) != 0)

                            t = par;                          // both done

                        else if ((b & state & SUMMED) != 0) { // both summed

                            int nextState; LongCumulateTask lt, rt;

                            if ((lt = par.left) != null &&

                                (rt = par.right) != null) {

                                long lout = lt.out;

                                par.out = (rt.hi == fnc ? lout :

                                           fn.applyAsLong(lout, rt.out));

                            }

                            int refork = (((b & CUMULATE) == 0 &&

                                           par.lo == org) ? CUMULATE : 0);

                            if ((nextState = b|state|refork) == b ||

                                par.compareAndSetPendingCount(b, nextState)) {

                                state = SUMMED;               // drop finished

                                t = par;

                                if (refork != 0)

                                    par.fork();

                            }

                        }

                        else if (par.compareAndSetPendingCount(b, b|state))

                            break outer;                      // sib not ready

                    }

                }

            }

        }

        @java.io.Serial

        private static final long serialVersionUID = -5074099945909284273L;

    }

    static final class DoubleCumulateTask extends CountedCompleter<Void> {

        final double[] array;

        final DoubleBinaryOperator function;

        DoubleCumulateTask left, right;

        double in, out;

        final int lo, hi, origin, fence, threshold;

        /** Root task constructor */

        public DoubleCumulateTask(DoubleCumulateTask parent,

                                  DoubleBinaryOperator function,

                                  double[] array, int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.lo = this.origin = lo; this.hi = this.fence = hi;

            int p;

            this.threshold =

                (p = (hi - lo) / (ForkJoinPool.getCommonPoolParallelism() << 3))

                <= MIN_PARTITION ? MIN_PARTITION : p;

        }

        /** Subtask constructor */

        DoubleCumulateTask(DoubleCumulateTask parent, DoubleBinaryOperator function,

                           double[] array, int origin, int fence, int threshold,

                           int lo, int hi) {

            super(parent);

            this.function = function; this.array = array;

            this.origin = origin; this.fence = fence;

            this.threshold = threshold;

            this.lo = lo; this.hi = hi;

        }

        public final void compute() {

            final DoubleBinaryOperator fn;

            final double[] a;

            if ((fn = this.function) == null || (a = this.array) == null)

                throw new NullPointerException();    // hoist checks

            int th = threshold, org = origin, fnc = fence, l, h;

            DoubleCumulateTask t = this;

            outer: while ((l = t.lo) >= 0 && (h = t.hi) <= a.length) {

                if (h - l > th) {

                    DoubleCumulateTask lt = t.left, rt = t.right, f;

                    if (lt == null) {                // first pass

                        int mid = (l + h) >>> 1;

                        f = rt = t.right =

                            new DoubleCumulateTask(t, fn, a, org, fnc, th, mid, h);

                        t = lt = t.left =

                            new DoubleCumulateTask(t, fn, a, org, fnc, th, l, mid);

                    }

                    else {                           // possibly refork

                        double pin = t.in;

                        lt.in = pin;

                        f = t = null;

                        if (rt != null) {

                            double lout = lt.out;

                            rt.in = (l == org ? lout :

                                     fn.applyAsDouble(pin, lout));

                            for (int c;;) {

                                if (((c = rt.getPendingCount()) & CUMULATE) != 0)

                                    break;

                                if (rt.compareAndSetPendingCount(c, c|CUMULATE)){

                                    t = rt;

                                    break;

                                }

                            }

                        }

                        for (int c;;) {

                            if (((c = lt.getPendingCount()) & CUMULATE) != 0)

                                break;

                            if (lt.compareAndSetPendingCount(c, c|CUMULATE)) {

                                if (t != null)

                                    f = t;

                                t = lt;

                                break;

                            }

                        }

                        if (t == null)

                            break;

                    }

                    if (f != null)

                        f.fork();

                }

                else {

                    int state; // Transition to sum, cumulate, or both

                    for (int b;;) {

                        if (((b = t.getPendingCount()) & FINISHED) != 0)

                            break outer;                      // already done

                        state = ((b & CUMULATE) != 0 ? FINISHED :

                                 (l > org) ? SUMMED : (SUMMED|FINISHED));

                        if (t.compareAndSetPendingCount(b, b|state))

                            break;

                    }

                    double sum;

                    if (state != SUMMED) {

                        int first;

                        if (l == org) {                       // leftmost; no in

                            sum = a[org];

                            first = org + 1;

                        }

                        else {

                            sum = t.in;

                            first = l;

                        }

                        for (int i = first; i < h; ++i)       // cumulate

                            a[i] = sum = fn.applyAsDouble(sum, a[i]);

                    }

                    else if (h < fnc) {                       // skip rightmost