javascript - 位操作 : detect if at least 5 bits in byte are set?

Question

检查二进制数是否设置了最小位数的最佳方法是什么？

例如，我需要查看此序列中是否至少有 5 位设置为 1:

101100010

我一直在研究使用位掩码之类的方法，但我对如何做到这一点感到困惑而不是自信。

感谢任何帮助。

Answer 1

来自 http://blog.faultylabs.com/2011.php?p=jsbitfun

/*
 popCnt(n)
 Returns the bit population count of n (that is: how many bits in n are set to 1)
 n must be an unsigned integer in the range [0..(2^32)-1]
 This lookup-table-free method is from Kernighan & Ritchie's "The C Programming Language"
 Exercise 2.9 (on page 62 of my copy). Not sure whether they (K&R) are the inventors.
*/
function popCnt(n) {
    n >>>= 0 /* force uint32 */
    for(var popcnt = 0; n; n &= n - 1) {
        popcnt++
    }
    return popcnt
}

参见 http://en.wikipedia.org/wiki/Hamming_weight有关其他算法的详细信息。