USERAPI StringHash

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This page documents a user-defined function that you can copy and paste into your addon. Replace <PREFIX> with your AddOn's prefix to avoid conflicts between different versions of these functions.

← User defined functions < StringHash

StringHash - by Mikk (talk • contr) -

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