将IP地址散列到[0，H）的数字中 [英] Hashing an IP address to a number in [0, H)

问题描述

我正在使用Python-2.6。我对散列函数知之甚少。

我想用一个CRC散列函数将一个IP地址如'128.0.0.5'散列到[0，H ）。目前我正在考虑购买

  zlib.crc32（'128.0.0.5'）％H。 
  

这样好吗？有几个问题。你可以尝试并回答... ...

• 它是否会产生任何差异。如果我散列'128.0.0.5'或其二进制'0001110101010 ..'，不论是否有'。'

，

• .zlib.crc32返回一个签名整数。修改（％）否定。有一个肯定的H总是给一个pos否？



• ％-ing by H是否会影响散列函数的良好性能？ （我的意思是，我可以做的最好的可用空间，可用xlib.crc32）

！

解决方案

它会产生任何差异。如果我散列'128.0.0.5'或其二进制'0001110101010 ..'，不论是否有'。'

真的。

zlib.crc32返回一个有符号的整数。修改（％）否定。一个积极的H总是给一个pos没有？

是。

％-ing by H是否影响散列函数的效果？ （我的意思是，我可以用可用空间做的最好的，可用的xlib.crc32）

你最好使用校验和的所有部分来弥补它们缺乏雪崩效应。诸如 192.168.1.1 ， 192.168.1.2 等一位数字的变体可能仅在前几位校验和，并且自％只关心最后一位，哈希将会发生冲突。

I'm using Python-2.6. I have very little knowledge of hash functions.

I want to use a CRC hash function to hash an IP address like '128.0.0.5' into the range [0, H). Currently I'm thinking of doing

zlib.crc32('128.0.0.5')%H.

Is this okay? There's a few ques. you could try and answer...

• does it make any diff. if I hash '128.0.0.5' or its binary '0001110101010..' whatever that is or without the '.'s

• zlib.crc32 returns a signed integer. Does modding (%) a neg. with a positive H always give a pos no?

• Does %-ing by H affect how good the hash function is? ( I mean is that the best I could do for the available space, with the available xlib.crc32)

Thanks!

解决方案

does it make any diff. if I hash '128.0.0.5' or its binary '0001110101010..' whatever that is or without the '.'s

Not really.

zlib.crc32 returns a signed integer. Does modding (%) a neg. with a positive H always give a pos no?

Yes.

Does %-ing by H affect how good the hash function is? ( I mean is that the best I could do for the available space, with the available xlib.crc32)

You'd better use all the bits of the checksum to make up for their lack of an "avalanche effect". Single-digit variations such as 192.168.1.1, 192.168.1.2, etc might produce differences only in the first bits of the checksum, and since % cares only about the last bits, hashes will collide.

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