StringHash

StringHash - by -

Return a fair-quality 32-bit hash of a string

hashVal = StringHash("string")

Example
> print(StringHash("")) 1 > print(StringHash("ab")) 3458343178 > print(StringHash("ba")) 3466747145 > print(StringHash("AB")) 2653593770 > print(StringHash("BA")) 2661997737 > print(StringHash("The quick brown fox jumps over the lazy dog")) 3402772626

Details

 * This algorithm is ~30% faster than a Lua implementation of the Java String.hashCode library call


 * The bit transmutation patterns and resulting collision rates are MUCH better than the results from the Java hash


 * See StringHash/Analysis

Code
local function StringHash(text) local counter = 1 local len = string.len(text) for i = 1, len, 3 do     counter = math.fmod(counter*8161, 4294967279) +  -- 2^32 - 17: Prime! (string.byte(text,i)*16776193) + ((string.byte(text,i+1) or (len-i+256))*8372226) + ((string.byte(text,i+2) or (len-i+256))*3932164) end return math.fmod(counter, 4294967291) -- 2^32 - 5: Prime (and different from the prime in the loop) end