散列函数增量是什么意思？ [英] What does it mean for a hash function to be incremental?

问题描述

我听说，例如，MurmurHash2不是增量，但MurmurHash3是增量式的。这是什么意思？为什么它很有用？

解决方案

增量散列函数适用于如果以前
散列消息，M稍微更新为新消息M *，那么它
应该相当快地计算更新的
消息的散列值M *。这是通过计算来自旧的
散列值m的新散列m *来完成的，与传统散列函数必须从
重新计算新散列m *相比，它需要从头开始更长的时间。

http://www.cs.berkeley.edu/~daw/papers/inchash-cs06.pdf

它们很有用，因为它们更容易计算，因此在计算能力和时间方面更便宜。

然而，它们不适合每一种情况。伯克利的这篇论文提供了一些很好的例子，介绍它们在介绍部分的用处。

I have heard that, for example, MurmurHash2 is not "incremental" but MurmurHash3 is incremental. What does this mean? And why is it useful?

解决方案

Incremental hash functions suited for situations where if a previously hashed message, M is slightly updated into a new message, M*, then it should be fairly quick to compute the hash value of the updated message, M*. This is done by computing the new hash, m*, from the old hash value, m, in contrast to conventional hash functions that have to recompute the new hash, m* from scratch, which takes a longer time.

http://www.cs.berkeley.edu/~daw/papers/inchash-cs06.pdf

They're useful due to the fact that they're easier to compute and therefore less expensive in terms of computing power and time.

However they're not suited to every situation. That paper from Berkeley has some nice examples of when they can be useful in the Introduction section.

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