hash.wyhash: implement rand function from wyhash original impl

vlib/hash/wyhash/rand.v

@@ -0,0 +1,14 @@
+// Copyright (c) 2019-2020 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+module wyhash
+
+pub fn rand_u64(seed &u64) u64 {
+	mut seed0 := seed
+	unsafe{
+		mut seed1 := *seed0
+		seed1+=wyp0
+		*seed0 = seed1
+		return wymum(seed1^wyp1, seed1)
+	}
+}

vlib/hash/wyhash/wyhash_test.v

@@ -27,3 +27,15 @@ fn test_wyhash() {
 		assert got == test.expected
 	}
 }
+
+fn test_rand_u64() {
+	seed := u64(111)
+	mut rand_nos := []u64
+	for _ in 0..40 {
+		rand_no := wyhash.rand_u64(&seed)
+		for r in rand_nos {
+			assert rand_no != r
+		}
+		rand_nos << rand_no
+	}
+}