Does NOT Hash128.Parse() method return UNIQUE hash?

Questions & Answers
1

Hi Dev!
For using Hash128 in my code, I tested some simple code. But result was a little weired.
I guessed Hash128.Parse() method returns UNIQUE hash (Hash128), but it didn’t.

Test code is below.

	Hash128 a = Hash128.Parse("TestA");
	Hash128 b = Hash128.Parse("TestB");
	
	Debug.Log( "a: " + a.ToString() );
	Debug.Log( "b: " + b.ToString() );
	Debug.Log( "equal? " + a.Equals( b ) );

And here is result log.

    a: 0e000000000000000000000000000000
    b: 0e000000000000000000000000000000
    equal? True

Do I use Hash128 wrong?

If do that, Please tell me how to use Hash128 correctly or hash function used for Hash128.
Thx!

3

Here’s an update. It looks like you can use Hash128’s Compute method with one of the various overloads. @Bunny83 It appears that Unity is using the SpookyV2 hashing algorithm, also mentioned in the link I shared.

2

No Hash128 is just a struct to store an AssetBundle hash. It can’t calculate a new hash. Parse is just the opposite of ToString. So all “Parse” does is convert the string representation of a hash back into the numeric struct representation. Again, it does not calculate a hash.

Just to make it more clear, here’s an example. I just created an arbitary hash manually and let it convert to string:

var h = new Hash128(0x12345678,0xABCDABCD,0xDEADBEAF, 0x55AA55AA);
string str = h.ToString();
Debug.Log("str: " + str);
var h2 = Hash128.Parse(str);
Debug.Log("equal? " + (h == h2));

In the console you will see:

str: 78563412cdabcdabafbeaddeaa55aa55

and

equal? True

As you can see ToString simply converts the 4 uint values into hex and Parse simply does the inverse and converts the hexadecimal representation back to a hash.

In your case “TestA” is not a valid hex string. However it actually detected the “e” in your string as hex digit which is the only one it can read.