在 Integer.java 和 Long.java 的源代码中,在大多数的 bit twiddling 方法中,都有一个名为“HD”的注释引用。每种方法都指向所述参考文献的特定部分。
那参考是什么?
highestOneBit(int)
这是类方法中的示例(此处Integer
为源代码,第 1035 行):
/**
* Returns an {@code int} value with at most a single one-bit, in the
* position of the highest-order ("leftmost") one-bit in the specified
* {@code int} value. Returns zero if the specified value has no
* one-bits in its two's complement binary representation, that is, if it
* is equal to zero.
*
* @return an {@code int} value with a single one-bit, in the position
* of the highest-order one-bit in the specified value, or zero if
* the specified value is itself equal to zero.
* @since 1.5
*/
public static int highestOneBit(int i) {
// HD, Figure 3-1
i |= (i >> 1);
i |= (i >> 2);
i |= (i >> 4);
i |= (i >> 8);
i |= (i >> 16);
return i - (i >>> 1);
}