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QuestDB is High Performance Time Series Database
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 * Copyright (C) 2014-2016 Appsicle
 *
 * This program is free software: you can redistribute it and/or  modify
 * it under the terms of the GNU Affero General Public License, version 3,
 * as published by the Free Software Foundation.
 *
 * 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 Affero General Public License for more details.
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package com.questdb.std;

import com.questdb.misc.Unsafe;

public class IntPriorityQueue {
    private int[] buffer;
    private int limit;

    public IntPriorityQueue() {
        this(8);
    }

    private IntPriorityQueue(int size) {
        this.buffer = new int[size];
        this.limit = 0;
    }

    public void clear() {
        limit = 0;
    }

    public boolean notEmpty() {
        return limit > 0;
    }

    public int pop() {
        int v = Unsafe.arrayGet(buffer, 0);
        if (--limit > 0) {
            System.arraycopy(buffer, 1, buffer, 0, limit);
        }
        return v;
    }

    public void push(int value) {
        int p = binSearch(value);
        if (p < limit) {
            System.arraycopy(buffer, p, buffer, p + 1, limit - p);
        }
        if (p >= buffer.length) {
            resize();
        }
        Unsafe.arrayPut(buffer, p, value);
        limit++;
    }

    private int binSearch(int v) {
        if (limit < 65) {
            return scanSearch(v);
        } else {
            return binSearch0(v);
        }
    }

    @SuppressWarnings("StatementWithEmptyBody")
    private int binSearch0(int v) {
        int low = 0;
        int high = limit;

        while (low < high) {

            if (high - low < 65) {
                return scanSearch(v);
            }

            int mid = (low + high - 1) >>> 1;
            int midVal = Unsafe.arrayGet(buffer, mid);

            if (midVal < v)
                low = mid + 1;
            else if (midVal > v)
                high = mid;
            else {
                for (; ++mid < high && Unsafe.arrayGet(buffer, mid) == v; ) ;
                return mid;
            }
        }
        return low;
    }

    private void resize() {
        int tmp[] = new int[buffer.length * 2];
        System.arraycopy(buffer, 0, tmp, 0, buffer.length);
        buffer = tmp;
    }

    private int scanSearch(int v) {
        for (int i = 0; i < limit; i++) {
            if (Unsafe.arrayGet(buffer, i) > v) {
                return i;
            }
        }
        return limit;
    }
}