Java java.lang.Integer class中的代码注释'HD, Figure'是什么意思？

Question

例如，JDK 方法 java.lang.Integer.numberOfLeadingZeros(int):

public static int numberOfLeadingZeros(int i) {
    // HD, Figure 5-6
    if (i == 0)
        return 32;
    int n = 1;
    if (i >>> 16 == 0) { n += 16; i <<= 16; }
    if (i >>> 24 == 0) { n +=  8; i <<=  8; }
    if (i >>> 28 == 0) { n +=  4; i <<=  4; }
    if (i >>> 30 == 0) { n +=  2; i <<=  2; }
    n -= i >>> 31;
    return n;
}

代码注释'HD，图5-6'是什么意思？

Answer 1

HD = 黑客的喜悦。见 the javadoc:

Implementation note: The implementations of the "bit twiddling" methods (such as highestOneBit and numberOfTrailingZeros) are based on material from Henry S. Warren, Jr.'s Hacker's Delight, (Addison Wesley, 2002).

Answer 2

java.lang.Long和java.lang.Math也有这样的评论。

例如java.lang.Math中的addExact方法：

public static int addExact(int x, int y) {
    int r = x + y;
    // HD 2-12 Overflow iff both arguments have the opposite sign of the result
    if (((x ^ r) & (y ^ r)) < 0) {
        throw new ArithmeticException("integer overflow");
    }
    return r;
}

Hacker's Delight的相关信息也可以参考：http://hackersdelight.org/

Java java.lang.Integer class中的代码注释'HD, Figure'是什么意思？

What does the code comment 'HD, Figure' mean in Java java.lang.Integer class?

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