From 1da862044e500de24e0dd6db42116248c7302e19 Mon Sep 17 00:00:00 2001
From: Alex Schneider <alex.schneider@sevenval.com>
Date: Fri, 7 Feb 2020 09:35:43 +0100
Subject: [PATCH] Faster and dependency-free MurmurHash3_32 implementation
---
murmur32.go | 61 ++++++++++++++++++++++++-----------------------------
1 file changed, 27 insertions(+), 34 deletions(-)
diff --git a/murmur32.go b/murmur32.go
index 552976a..9a6e3c0 100644
--- a/murmur32.go
+++ b/murmur32.go
@@ -18,6 +18,9 @@ var (
const (
c1_32 uint32 = 0xcc9e2d51
c2_32 uint32 = 0x1b873593
+ c3_32 uint32 = 0x85ebca6b
+ c4_32 uint32 = 0xc2b2ae35
+ c5_32 uint32 = 0xe6546b64
)
// digest32 represents a partial evaluation of a 32 bites hash.
@@ -114,49 +117,39 @@ func Sum32WithSeed(data []byte, seed uint32) uint32 {
h1 := seed
- nblocks := len(data) / 4
- var p uintptr
- if len(data) > 0 {
- p = uintptr(unsafe.Pointer(&data[0]))
- }
- p1 := p + uintptr(4*nblocks)
- for ; p < p1; p += 4 {
- k1 := *(*uint32)(unsafe.Pointer(p))
-
- k1 *= c1_32
- k1 = bits.RotateLeft32(k1, 15)
- k1 *= c2_32
+ dlen := len(data)
+ var k uint32
- h1 ^= k1
- h1 = bits.RotateLeft32(h1, 13)
- h1 = h1*4 + h1 + 0xe6546b64
+ for i := dlen >> 2; i != 0; i-- {
+ k = uint32(data[0])<<24 | uint32(data[1])<<16 | uint32(data[2])<<8 | uint32(data[3])
+ data = data[4:]
+ h1 ^= mix(k)
+ h1 = (h1 << 13) | (h1 >> 19)
+ h1 = h1*5 + c5_32
}
- tail := data[nblocks*4:]
-
- var k1 uint32
- switch len(tail) & 3 {
- case 3:
- k1 ^= uint32(tail[2]) << 16
- fallthrough
- case 2:
- k1 ^= uint32(tail[1]) << 8
- fallthrough
- case 1:
- k1 ^= uint32(tail[0])
- k1 *= c1_32
- k1 = bits.RotateLeft32(k1, 15)
- k1 *= c2_32
- h1 ^= k1
+ k = 0
+ for i := dlen & 3; i != 0; i-- {
+ k <<= 8
+ k |= uint32(data[i-1])
}
- h1 ^= uint32(len(data))
+ h1 ^= mix(k)
+ h1 ^= uint32(dlen)
h1 ^= h1 >> 16
- h1 *= 0x85ebca6b
+ h1 *= c3_32
h1 ^= h1 >> 13
- h1 *= 0xc2b2ae35
+ h1 *= c4_32
h1 ^= h1 >> 16
return h1
}
+
+func mix(k uint32) uint32 {
+ k *= c1_32
+ k = (k << 15) | (k >> 17)
+ k *= c2_32
+
+ return k
+}