compiler: refactor compiler into separate package

compiler/util.go

@@ -0,0 +1,26 @@
+package compiler
+
+// This file contains functions that are also used by the runtime. These must be
+// kept in sync.
+
+// Get FNV-1a hash of this string.
+//
+// https://en.wikipedia.org/wiki/Fowler%E2%80%93Noll%E2%80%93Vo_hash_function#FNV-1a_hash
+func hashmapHash(data []byte) uint32 {
+	var result uint32 = 2166136261 // FNV offset basis
+	for _, c := range data {
+		result ^= uint32(c)
+		result *= 16777619 // FNV prime
+	}
+	return result
+}
+
+// Get the topmost 8 bits of the hash, without using a special value (like 0).
+func hashmapTopHash(hash uint32) uint8 {
+	tophash := uint8(hash >> 24)
+	if tophash < 1 {
+		// 0 means empty slot, so make it bigger.
+		tophash += 1
+	}
+	return tophash
+}