javascript - 哈希分布，为什么 0 总是重权重？

Question

我写了一个快速的 Canvas 可视化来查看我从 C++ 移植到 JavaScript 的哈希算法的分布。

我看到奇怪的行为，无论我用什么修改散列，0 都是严重有偏见的，因为它被选择的频率是散列函数中大多数其他数字的两倍。

您可以在以下位置查看演示:http://jsfiddle.net/x5L73/2/

和原始的 C++ 算法:http://www.azillionmonkeys.com/qed/hash.html

我所指的代码部分位于 jsFiddle 的底部:

// hash is 0 twice as often as anything else
var hash = app.Hash( word ) % ( 3499 )
  ,   b1 = 0|hash / 59
  ,   b2 =   hash % 59;

对我来说奇怪的是 hash 为零的频率是 any 其他值的两倍，无论我选择用什么来修改它。在此示例中，它是零 1/3499 次，而 任何 其他数字被命中 1/6998 次。这是通过暴力测试确定的:

if( hash!==1234 ){ nonZero++; }else{ zero++ } // 1234 is a random number to check       
if( Math.random() < .00001 ){ console.log( zero, nonZero, 0|nonZero/zero ); }

我在这里错过了什么？？？

Answer 1

虽然这是一个非常有趣的事实，在处理整数时可能会派上用场，就像哈希一样，但错误是不是，因为 JavaScript 有负零也是...

OP 报告的原始原因是:

It's because I was accidentally discarding all negative numbers in the visualization.

是的，负数并不是那么微不足道，我们的大脑有时会忽略它们 - 特别是当他们长时间专注于涉及整数的特定难题时，就像试图找出好的哈希方法，然后切换一个看似简单得多的任务:显示结果...

所以真正的答案是:除了负零之外，JavaScript 还有更多的负数......不要忘记将它们计算在内 - 即使在easy 可视化任务。

长话短说

我把它留在这里，因为这可能对将来遇到类似问题的任何人都有用，因为它可能会导致类似的情况。

看这个问题:+0 and -0 in JavaScript (negative zero and positive zero in JavaScript)

引用:

JavaScript uses IEEE 745 standard to represent numbers. From Wikipedia:

Signed zero is zero with an associated sign. In ordinary arithmetic, −0 = +0 = 0. However, in computing, some number representations allow for the existence of two zeros, often denoted by −0 (negative zero) and +0 (positive zero). This occurs in some signed number representations for integers, and in most floating point number representations. The number 0 is usually encoded as +0, but can be represented by either +0 or −0.

The IEEE 754 standard for floating point arithmetic (presently used by most computers and programming languages that support floating point numbers) requires both +0 and −0. The zeroes can be considered as a variant of the extended real number line such that 1/−0 = −∞ and 1/+0 = +∞, division by zero is only undefined for ±0/±0 and ±∞/±∞.