jhash

jhash() -- hash a variable-length key into a 32-bit value

k : the key (the unaligned variable-length array of bytes) len : the length of the key, counting by bytes level : can be any 4-byte value

Returns a 32-bit value. Every bit of the key affects every bit of the return value. Every 1-bit and 2-bit delta achieves avalanche.

About 4.3*len + 80 X86 instructions, with excellent pipelining

The best hash table sizes are powers of 2. There is no need to do mod a prime (mod is sooo slow!). If you need less than 32 bits, use a bitmask. For example, if you need only 10 bits, do

h = (h & hashmask(10));

In which case, the hash table should have hashsize(10) elements. If you are hashing n strings (ub1 **)k, do it like this:

for (i=0, h=0; i<n; ++i) h = hash( ki, leni, h);

By Bob Jenkins, 1996. bob_jenkins@burtleburtle.net. You may use this code any way you wish, private, educational, or commercial. It's free.

See http://burtleburtle.net/bob/hash/evahash.html Use for hash table lookup, or anything where one collision in 2^32 is acceptable. Do NOT use for cryptographic purposes.

  1. size_t jhash(ubyte* k, size_t len, size_t c)
    size_t
    jhash
    (
    ubyte* k
    ,
    size_t len
    ,
    size_t c = 0
    )
  2. size_t jhash(void[] x, size_t c)

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