variable precision SWAR算法

经典Redis中BITCOUNT命令的算法

原理可以看这篇博客

variable precision SWAR算法

public class JZ11 {
    public int NumberOf1(int n) {
        n = (n & 0x55555555) + ((n >> 1) & 0x55555555);
        n = (n & 0x33333333) + ((n >> 2) & 0x33333333);
        n = (n & 0x0F0F0F0F) + ((n >> 4) & 0x0F0F0F0F);
        n = ((n * 0x01010101) >> 24);
        return n;
    }

    @Test
    public void Test() {
        Assert.assertEquals(NumberOf1(10), 2);
        Assert.assertEquals(NumberOf1(0),0);
        Assert.assertEquals(NumberOf1(Integer.MAX_VALUE), 31);
        Assert.assertEquals(NumberOf1(Integer.MIN_VALUE), 1);
        Assert.assertEquals(NumberOf1(-1),32);
    }
}