Java Array Size Get arraySize(final int expected, final float f)

Description

array Size

License

Open Source License

Declaration

public static int arraySize(final int expected, final float f) 

Method Source Code

//package com.java2s;
/*/*from  ww w .ja v  a2 s .co m*/
 * Copyright (c) 2017 VMware Inc. All Rights Reserved.
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

public class Main {
    public static int arraySize(final int expected, final float f) {
        final long s = Math.max(2L, nextPowerOfTwo((long) Math.ceil((double) ((float) expected / f))));
        if (s > 1073741824L) {
            throw new IllegalArgumentException(
                    "Too large (" + expected + " expected elements with load factor " + f + ")");
        } else {
            return (int) s;
        }
    }

    public static int nextPowerOfTwo(int x) {
        if (x == 0) {
            return 1;
        } else {
            --x;
            x |= x >> 1;
            x |= x >> 2;
            x |= x >> 4;
            x |= x >> 8;
            return (x | (x >> 16)) + 1;
        }
    }

    private static long nextPowerOfTwo(long x) {
        if (x == 0L) {
            return 1L;
        } else {
            --x;
            x |= x >> 1;
            x |= x >> 2;
            x |= x >> 4;
            x |= x >> 8;
            x |= x >> 16;
            return (x | (x >> 32)) + 1L;
        }
    }
}

Related

1. arraySize(final int expected, final float f)
2. arraySizeOf(int[] array)