[chinpokomon]

To implement the hash table you wouldn't have to hash the whole string... of course this will depend on the data that you are trying to store. Assuming that the data is random, 100 bytes vs. 100 terabytes, you only need to figure out what bucket the data is saved. You could still base it on this concept if sightly modified

[rnovak]

Yes. A valid hash function certainly can be defined as a F(n): N x N -> n % 100

But that certainly cannot be considered a reasonable hash function. A string is basically an array of bytes (or code-points, in case of UTF-8).

To have any decent property (like, producing different outputs for miniscule changes in the input), you have to touch every element in the array.

For custom objects, yes, you don't have to hash every property, but for strings, yeah, the hash function will almost always depend on the length of the string.