I'm trying to write my own hash function that uses a 30-bit hash.
Here is some code for a FNVa 32-bit hash.
func fnva32(data string) uint32 {
var hash uint32 = 2166136261
for _, c := range data {
hash ^= uint32(c)
hash *= 16777619
}
return hash
}
Now here is my code that converts lowercase letters a-z into a 30-bit hash:
func id(s string) uint {
var id uint
var power uint = 1
for _, c := range s {
id+=(uint(c)-96)*power
power*=26
}
return id%1073741824
}
That specifically limits my hash function to a maximum of 30-bit because I'm using a modulus against that number. But how is that FNVa32 hash limited to 32-bits? They are not using a modulus. How does it not generate a number larger than that?
Also you probably notice that I'm not using prime numbers. I tried some prime numbers but it increased the collisions. Currently I'm getting 291 collisions and FNVa32 is getting 76 collisions, from hashing 600,000 (real) words.
My question is... what is making FNVa32 limit to 32-bit, and how would I change it to be 30-bit instead?
