chore: move from tools/dsa (#1)

Moved the implementation of this hash table from `tools/dsa` #1.

Reviewed-on: #1
Co-authored-by: M.V. Hutz <git@maximhutz.me>
Co-committed-by: M.V. Hutz <git@maximhutz.me>

hash.go

@@ -0,0 +1,27 @@
+package cuckoo
+
+import (
+	"hash/maphash"
+)
+
+// A Hash function maps any data to a fixed-length value (in this case, a
+// [uint64]).
+//
+// It is used by the [Table] to evenly distribute values
+// amongst its slots. A good hash function is uniform, [chaotic], and
+// deterministic. [Table] uses [NewDefaultHash] by default, which is built on
+// [maphash.Comparable].
+//
+// [chaotic]: https://en.wikipedia.org/wiki/Avalanche_effect
+type Hash[K any] = func(key K) (digest uint64)
+
+// NewDefaultHash returns a new [Hash] which uses [maphash.Comparable].
+//
+// Each hash has a random seed, so calling this function again will return a new
+// hash. Do not use this for testing.
+func NewDefaultHash[K comparable]() Hash[K] {
+	seed := maphash.MakeSeed()
+	return func(key K) (digest uint64) {
+		return maphash.Comparable(seed, key)
+	}
+}