java - Java 类 Integer 和 Long 的源代码中的 "HD"是什么意思？

Question

在 Integer.java 和 Long.java 的源代码中，在大多数位旋转方法中，有一个对称为“HD”的东西的注释引用。每个方法都指向所述引用的特定部分。

那个引用是什么？

下面是 Integer 类的方法 highestOneBit(int) 中的示例(源代码 here，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);
}

Answer 1

来自源码顶部的注释...

   40    * <p>Implementation note: The implementations of the "bit twiddling"
   41    * methods (such as {@link #highestOneBit(int) highestOneBit} and
   42    * {@link #numberOfTrailingZeros(int) numberOfTrailingZeros}) are
   43    * based on material from Henry S. Warren, Jr.'s <i>Hacker's
   44    * Delight</i>, (Addison Wesley, 2002).
   45    *

Hacker's Delight亨利·沃伦 (Henry S. Warren)。