Hash value

[jimhce]

Hi,

I want to generate a hash key from a string, and I want to the hash key is the same value for the same string. But it turns out all the hash functions I have tried, generate different keys from the same string. For example, if I run an excusable hash function several times in following example, it gave me all different values even the string does not change:

$ BobJenkinHash "hello"
0x183B3443

$ BobJenkinHash "hello"
0x24082445

Is it possible to generate the same hash value based on the same string?

Thank you.

Jim

[gpraghuram]

Hi,

I want to generate a hash key from a string, and I want to the hash key is the same value for the same string. But it turns out all the hash functions I have tried, generate different keys from the same string. For example, if I run an excusable hash function several times in following example, it gave me all different values even the string does not change:

$ BobJenkinHash "hello"
0x183B3443

$ BobJenkinHash "hello"
0x24082445

Is it possible to generate the same hash value based on the same string?

Thank you.

Jim

Have u heard about CRC, if yes then that can help u.
Try to use 32-bit crc(the code for this is available in net).
This will generate a unsigned long nu,ber for every input string u give.

Raghuram

[jimhce]

Could you point me the URL?

Thank you.

Jim

[weaknessforcats]

Also, if your hash does result in the same value for multiple keys, you can use a chain-link table to handle this. That is, of your are not using a chain-link table already.

Any hashing algorithm will produce the same value for multiple keys. The chain-link table is only way to handle the one-to-many relataionship. You can also use a vector of vectors.

[JosAH]

Any hashing algorithm will produce the same value for multiple keys. The chain-link table is only way to handle the one-to-many relataionship.

That is not true; hash functions exist that are 'perfect', i.e. for any different pair
of keys k_i and k_j, h(k_i) != h(k_j); there even exist 'minimal perfect hash
functions where h(x) in [1, |x|]; but the set of keys k_i has to be known in
advance so h() can be computed.

kind regards,

Jos