Tweak hash (#14)

src/weather/key.rs

@@ -7,9 +7,19 @@ impl Key {
     pub fn new(bytes: &[u8]) -> Self {
         // djb2 hash fn
         // hash(0) = 5381
-        // hash(i) = hash(i-1) * 33 ^ byte[i]
-        let hash_fn = |hash, byte: &u8| (hash * 33) ^ u64::from(*byte);
-        Self(bytes.iter().fold(5381, hash_fn))
+        // hash(i) = hash(i-1) * 33 + byte[i]
+        let hash_fn = |hash: u64, &byte| hash.wrapping_mul(33).wrapping_add(byte as u64);
+
+        let len = bytes.len();
+        let first = &bytes[..len.min(8)];
+        let last = if len > 8 { &bytes[len - 8..] } else { &[] };
+        Self(
+            first
+                .iter()
+                .chain(last)
+                .fold(5381, hash_fn)
+                .wrapping_mul(len as u64), // multiply with the length of input to ensure no collisions
+        )
     }
 }