Java Bit Count countBits(final int intValue)

Description

Counts the number of 1-Bits in a 32-bit int value and uses a "divide-and-conquer" strategy.

License

Apache License

Parameter

Parameter	Description
intValue	int value.

Return

Number of 1-Bits.

Declaration

public static int countBits(final int intValue) 

Method Source Code

//package com.java2s;
/*/*  w ww  .j  a v a2s.  c om*/
 * Copyright 2013, Carsten J?ger
 *
 * 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 {
    /**
     * Constant 4.
     */
    public static final byte CONST_4 = 4;
    /**
     * Constant 8.
     */
    public static final byte CONST_8 = 8;

    /**
     * Counts the number of 1-Bits in a 32-bit int value and uses a "divide-and-conquer" strategy. (see Hacker's
     * Delight, Section 5.1).
     *
     * @param intValue int value.
     * @return Number of 1-Bits.
     */
    public static int countBits(final int intValue) {
        final byte const16 = 16;
        final byte const3F = 0x0000003F;
        final int const33 = 0x33333333;
        final int const55 = 0x55555555;
        final int const0F = 0x0F0F0F0F;
        int result = intValue;
        result -= ((result >>> 1) & const55);
        result = (result & const33) + ((result >>> 2) & const33);
        result = (result + (result >>> CONST_4)) & const0F;
        result += (result >>> CONST_8);
        result += (result >>> const16);
        return result & const3F;
    }
}

Related

1. bitLength(int value)
2. bitSizeForSignedValue(final int value)
3. bitSizeForUnsignedValue(final int value)
4. countBits (long v)
5. countBits(byte num)
6. countBits(int i)
7. countBits(int mask)
8. countBits(int n)
9. countBits(int x)