WoW:USERAPI StringHash: Difference between revisions
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StringHash - by Template:User -
(→Code: "mod" -> "math.mod" so it works outside of wow) |
(→Code: W/ the 2.0 changes, lua 5.1 renamed math.mod to math.fmod) |
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| Line 35: | Line 35: | ||
local len = string.len(text); | local len = string.len(text); | ||
for i = 1, len, 3 do | for i = 1, len, 3 do | ||
counter = math. | counter = math.fmod(counter*8161, 4294967279) + -- 2^32 - 17: Prime! | ||
(string.byte(text,i)*16776193) + | (string.byte(text,i)*16776193) + | ||
((string.byte(text,i+1) or (len-i+256))*8372226) + | ((string.byte(text,i+1) or (len-i+256))*8372226) + | ||
((string.byte(text,i+2) or (len-i+256))*3932164); | ((string.byte(text,i+2) or (len-i+256))*3932164); | ||
end; | end; | ||
return math. | return math.fmod(counter, 4294967291); -- 2^32 - 5: Prime (and different from the prime in the loop) | ||
end | end | ||
Revision as of 21:41, 12 January 2007
This page documents a user-defined function that you can copy and paste into your addon. Replace PREFIX with your addon or lib prefix to avoid conflicts between different versions of these functions.
Return a fair-quality 32-bit hash of a string
hashVal = <PREFIX>_StringHash("string")
Example
> print(PREFIX_StringHash(""))
1
> print(<PREFIX>_StringHash("ab"))
3458343178
> print(<PREFIX>_StringHash("ba"))
3466747145
> print(<PREFIX>_StringHash("AB"))
2653593770
> print(<PREFIX>_StringHash("BA"))
2661997737
> print(<PREFIX>_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
Code
function <PREFIX>_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