add vendor

vendor/github.com/segmentio/fasthash/fnv1a/hash.go

@@ -0,0 +1,71 @@
+package fnv1a
+
+const (
+	// FNV-1a
+	offset64 = uint64(14695981039346656037)
+	prime64  = uint64(1099511628211)
+
+	// Init64 is what 64 bits hash values should be initialized with.
+	Init64 = offset64
+)
+
+// HashString64 returns the hash of s.
+func HashString64(s string) uint64 {
+	return AddString64(Init64, s)
+}
+
+// HashUint64 returns the hash of u.
+func HashUint64(u uint64) uint64 {
+	return AddUint64(Init64, u)
+}
+
+// AddString64 adds the hash of s to the precomputed hash value h.
+func AddString64(h uint64, s string) uint64 {
+	/*
+		This is an unrolled version of this algorithm:
+
+		for _, c := range s {
+			h = (h ^ uint64(c)) * prime64
+		}
+
+		It seems to be ~1.5x faster than the simple loop in BenchmarkHash64:
+
+		- BenchmarkHash64/hash_function-4   30000000   56.1 ns/op   642.15 MB/s   0 B/op   0 allocs/op
+		- BenchmarkHash64/hash_function-4   50000000   38.6 ns/op   932.35 MB/s   0 B/op   0 allocs/op
+
+	*/
+
+	i := 0
+	n := (len(s) / 8) * 8
+
+	for i != n {
+		h = (h ^ uint64(s[i])) * prime64
+		h = (h ^ uint64(s[i+1])) * prime64
+		h = (h ^ uint64(s[i+2])) * prime64
+		h = (h ^ uint64(s[i+3])) * prime64
+		h = (h ^ uint64(s[i+4])) * prime64
+		h = (h ^ uint64(s[i+5])) * prime64
+		h = (h ^ uint64(s[i+6])) * prime64
+		h = (h ^ uint64(s[i+7])) * prime64
+		i += 8
+	}
+
+	for _, c := range s[i:] {
+		h = (h ^ uint64(c)) * prime64
+	}
+
+	return h
+}
+
+// AddUint64 adds the hash value of the 8 bytes of u to h.
+func AddUint64(h uint64, u uint64) uint64 {
+	h = (h ^ ((u >> 56) & 0xFF)) * prime64
+	h = (h ^ ((u >> 48) & 0xFF)) * prime64
+	h = (h ^ ((u >> 40) & 0xFF)) * prime64
+	h = (h ^ ((u >> 32) & 0xFF)) * prime64
+	h = (h ^ ((u >> 24) & 0xFF)) * prime64
+	h = (h ^ ((u >> 16) & 0xFF)) * prime64
+	h = (h ^ ((u >> 8) & 0xFF)) * prime64
+	h = (h ^ ((u >> 0) & 0xFF)) * prime64
+	return h
+}