爪哇查找设置比特长

Question

我有一个很长的数字。现在，我要的是以下项目（以伪代码给出），

for each two bits of that long 

if the two bits == 11 

then count++ 

(for example if number is "11 01 10 00 11" it will give count = 2) 

任何人可以帮助我如何在Java中有效地做到这一点？

Answer 1

public static int count11(long n) { 
    int cnt = 0; 
    while (n != 0) { 
    if ((n & 3) == 3) cnt++; 
    n >>>= 2; 
    } 
    return cnt; 
} 

的更有效的变体：

public static int count11(long n) { 
    int cnt = 0; 
    while (n != 0) { 
    switch ((int)(n & 0x3F)) { 
    case 0x3F: cnt += 3; break; 
    case 0x3C: case 0x33: case 0xF: cnt += 2; break; 
    case 0x30: case 0xC: case 3: cnt++; 
    } 
    n >>>= 6; 
    } 
    return cnt; 
}