Initial project import

tools/v/vlib/hash/wyhash.v

@@ -0,0 +1,44 @@
+// Copyright (c) 2019-2024 Alexander Medvednikov. All rights reserved.
+// Use of this source code is governed by an MIT license
+// that can be found in the LICENSE file.
+//
+// this is an implementation of wyhash v4
+// from https://github.com/wangyi-fudan/wyhash
+//
+// TODO: use u128 once implemented
+// currently the C version performs slightly better
+// because it uses 128 bit int when available and
+// branch prediction hints. the C version will be
+// removed once the performance is matched.
+// you can test performance by running:
+// `v run cmd/tools/bench/wyhash.v`
+// try running with and without the `-prod` flag
+module hash
+
+const wyp0 = u64(0x2d358dccaa6c78a5)
+const wyp1 = u64(0x8bb84b93962eacc9)
+const wyp2 = u64(0x4b33a62ed433d4a3)
+const wyp3 = u64(0x4d5a2da51de1aa47)
+
+// wymum returns a hash by performing multiply and mix on `a` and `b`.
+@[ignore_overflow; inline]
+pub fn wymum(a u64, b u64) u64 {
+	/*
+	mut r := u128(a)
+	r = r*b
+	return (r>>64)^r
+	*/
+	mask32 := u32(4294967295)
+	x0 := a & mask32
+	x1 := a >> 32
+	y0 := b & mask32
+	y1 := b >> 32
+	w0 := x0 * y0
+	t := x1 * y0 + (w0 >> 32)
+	mut w1 := t & mask32
+	w2 := t >> 32
+	w1 += x0 * y1
+	hi := x1 * y1 + w2 + (w1 >> 32)
+	lo := a * b
+	return hi ^ lo
+}