reversing a hash function

From: Skybuck Flying (nospam_at_hotmail.com)
Date: 08/27/04 

Date: Fri, 27 Aug 2004 19:49:27 +0200

Hi,

I have this hash function:

function function_hash(
 const a : word;
 const b : longword;
 const c : longword;
 const d : byte ) : longword;
 result :=
 (
  (
   ((a) shr 1) xor (b) xor (c) xor (d)
  ) and (63)
 );

Or for example in C:

#define function_hash (a, b, c, d) \
 ((((a) >> 1) ^ (b) ^ (c) ^ (d)) & (63))

These two hash functions are the same and will always produce a value
ranging from 0 to 63.

Let's say a, c, d and hash are known and b is unknown.
Is it possible to find all B for hash value X

For example

Find all hash values for B where a=1 c=2 and d=3 and hash=10.

I could ofcourse simply try out all values for B... but maybe there is a
faster way ?

Let's say a,c, hash are known and b,d are unknown.

Q2: Is it still possible to find all a, c where hash = x ?

For example a=1, c=2, hash = 10

I could ofcourse again try all possible values for b and d but again maybe
there is a faster way ?

Thanks for any help,
  Bye
     Skybuck.

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