util: Hash: avoid using bytes.Buffer and binary.Read to reduce allocations (fixes #141)
diff --git a/leveldb/util/hash.go b/leveldb/util/hash.go
index 5490366..7f3fa4e 100644
--- a/leveldb/util/hash.go
+++ b/leveldb/util/hash.go
@@ -7,38 +7,38 @@
package util
import (
- "bytes"
"encoding/binary"
)
// Hash return hash of the given data.
func Hash(data []byte, seed uint32) uint32 {
// Similar to murmur hash
- var m uint32 = 0xc6a4a793
- var r uint32 = 24
- h := seed ^ (uint32(len(data)) * m)
+ const (
+ m = uint32(0xc6a4a793)
+ r = uint32(24)
+ )
+ var (
+ h = seed ^ (uint32(len(data)) * m)
+ i int
+ )
- buf := bytes.NewBuffer(data)
- for buf.Len() >= 4 {
- var w uint32
- binary.Read(buf, binary.LittleEndian, &w)
- h += w
+ for n := len(data) - len(data)%4; i < n; i += 4 {
+ h += binary.LittleEndian.Uint32(data[i:])
h *= m
h ^= (h >> 16)
}
- rest := buf.Bytes()
- switch len(rest) {
+ switch len(data) - i {
default:
panic("not reached")
case 3:
- h += uint32(rest[2]) << 16
+ h += uint32(data[i+2]) << 16
fallthrough
case 2:
- h += uint32(rest[1]) << 8
+ h += uint32(data[i+1]) << 8
fallthrough
case 1:
- h += uint32(rest[0])
+ h += uint32(data[i])
h *= m
h ^= (h >> r)
case 0:
diff --git a/leveldb/util/hash_test.go b/leveldb/util/hash_test.go
new file mode 100644
index 0000000..a35d273
--- /dev/null
+++ b/leveldb/util/hash_test.go
@@ -0,0 +1,46 @@
+// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
+// All rights reserved.
+//
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package util
+
+import (
+ "testing"
+)
+
+var hashTests = []struct {
+ data []byte
+ seed uint32
+ hash uint32
+}{
+ {nil, 0xbc9f1d34, 0xbc9f1d34},
+ {[]byte{0x62}, 0xbc9f1d34, 0xef1345c4},
+ {[]byte{0xc3, 0x97}, 0xbc9f1d34, 0x5b663814},
+ {[]byte{0xe2, 0x99, 0xa5}, 0xbc9f1d34, 0x323c078f},
+ {[]byte{0xe1, 0x80, 0xb9, 0x32}, 0xbc9f1d34, 0xed21633a},
+ {[]byte{
+ 0x01, 0xc0, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x14, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x04, 0x00,
+ 0x00, 0x00, 0x00, 0x14,
+ 0x00, 0x00, 0x00, 0x18,
+ 0x28, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x00,
+ 0x02, 0x00, 0x00, 0x00,
+ 0x00, 0x00, 0x00, 0x00,
+ }, 0x12345678, 0xf333dabb},
+}
+
+func TestHash(t *testing.T) {
+ for i, x := range hashTests {
+ h := Hash(x.data, x.seed)
+ if h != x.hash {
+ t.Fatalf("test-%d: invalid hash, %#x vs %#x", i, h, x.hash)
+ }
+ }
+}
