packed: Write packs with deltas

1 files changed, 42 insertions, 0 deletions

diff --git a/internal/murmurhash2/murmurhash2.go b/internal/murmurhash2/murmurhash2.go
new file mode 100644
index 00000000..c728f932
--- /dev/null
+++ b/internal/murmurhash2/murmurhash2.go
@@ -0,0 +1,42 @@
+// Package murmurhash2 provides a non-cryptographic hash.
+package murmurhash2
+
+import "encoding/binary"
+
+// Sum32 computes the MurmurHash2 value for key with the provided seed.
+func Sum32(key []byte, seed uint32) uint32 {
+	const (
+		m uint32 = 0x5bd1e995
+		r uint32 = 24
+	)
+
+	h := seed ^ uint32(len(key))
+	i := 0
+	for len(key)-i >= 4 {
+		k := binary.LittleEndian.Uint32(key[i:])
+		k *= m
+		k ^= k >> r
+		k *= m
+
+		h *= m
+		h ^= k
+		i += 4
+	}
+
+	switch len(key) - i {
+	case 3:
+		h ^= uint32(key[i+2]) << 16
+		fallthrough
+	case 2:
+		h ^= uint32(key[i+1]) << 8
+		fallthrough
+	case 1:
+		h ^= uint32(key[i])
+		h *= m
+	}
+
+	h ^= h >> 13
+	h *= m
+	h ^= h >> 15
+	return h
+}