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hash function and combining function/operator in perl

+1 vote
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I'm looking for a hash function and a related function or operator such that:

 H(string1 . string2) = f(H(string1), H(string2))
 H(string1 . string2) = H(string1) op H(string2)

 where:
 H() is the hash function    
 string1 is a string
 string2 is a string    
 . is the string concatenation operator 
 f() is a function
 op is a binary operator

Any suggestions?

posted Sep 23, 2013 by Abhay Kulkarni

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1 Answer

+1 vote

My immediate thought is that the only hash function that can work like this is the identity function (or any one-one mapping) because, by extension, the hash of a string must be equal to f(the hash of each of
its characters).

Not that I can prove this at present, of course! Could you explain the problem you're trying to solve?

answer Sep 23, 2013 by Seema Siddique
Writing scripts that look for duplicate, similar, and/or missing files.
commented Sep 23, 2013 by anonymous
I don't know the answer but... it sounds like NCBI's BLAST to me, which compares nucleotide or protein sequences. NCBI's FTP site provides local BLAST binaries, and bioperl offers some convenient tools to implement it.
commented Sep 25, 2013 by anonymous
That looks like server-side software, callable via a WWW UI and/or Perl modules (?).
Where is the design documentation for BLAST -- especially the hashing algorithms?
commented Sep 25, 2013 by anonymous
Another look at it, and I think I've pointed you to a wrong way. BLAST might not what you need. Sorry about this.
commented Sep 26, 2013 by anonymous
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