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murmur.go
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murmur.go
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package murmur
import (
"encoding/binary"
)
const (
c1 uint32 = 0x239b961b
c2 uint32 = 0xab0e9789
c3 uint32 = 0x38b34ae5
c4 uint32 = 0xa1e38b93
)
func ROTL32(x uint32, r uint8) uint32 {
return (x << r) | (x >> (32 - r))
}
func fmix32 (h uint32) uint32 {
h ^= h >> 16
h *= 0x85ebca6b
h ^= h >> 13
h *= 0xc2b2ae35
h ^= h >> 16
return h
}
func getblock32 (p []byte, tailIndex int, i int) (result uint32) {
result = binary.LittleEndian.Uint32(p[tailIndex + (i * 4):])
return
}
func MurmurHash3_x86_128 (key []byte, seed uint32) (out [2]uint64) {
nblocks := len(key) / 16
// tail points just behind the last complete 32 bit block in the key
tailIndex := 16 * nblocks
tail := key[tailIndex:]
h1 := seed
h2 := seed
h3 := seed
h4 := seed
//----------
// body
for i := -nblocks; i != 0; i++ {
k1 := getblock32(key, tailIndex, i*4+0)
k2 := getblock32(key, tailIndex, i*4+1)
k3 := getblock32(key, tailIndex, i*4+2)
k4 := getblock32(key, tailIndex, i*4+3)
k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
h1 = ROTL32(h1,19); h1 += h2; h1 = h1*5+0x561ccd1b;
k2 *= c2; k2 = ROTL32(k2,16); k2 *= c3; h2 ^= k2;
h2 = ROTL32(h2,17); h2 += h3; h2 = h2*5+0x0bcaa747;
k3 *= c3; k3 = ROTL32(k3,17); k3 *= c4; h3 ^= k3;
h3 = ROTL32(h3,15); h3 += h4; h3 = h3*5+0x96cd1c35;
k4 *= c4; k4 = ROTL32(k4,18); k4 *= c1; h4 ^= k4;
h4 = ROTL32(h4,13); h4 += h1; h4 = h4*5+0x32ac3b17;
}
//----------
// tail
k1 := uint32(0)
k2 := uint32(0)
k3 := uint32(0)
k4 := uint32(0)
switch len(key) & 15 {
case 15: k4 ^= uint32(tail[14]) << 16; fallthrough
case 14: k4 ^= uint32(tail[13]) << 8; fallthrough
case 13: k4 ^= uint32(tail[12]) << 0
k4 *= c4; k4 = ROTL32(k4,18); k4 *= c1; h4 ^= k4;
fallthrough
case 12: k3 ^= uint32(tail[11]) << 24; fallthrough
case 11: k3 ^= uint32(tail[10]) << 16; fallthrough
case 10: k3 ^= uint32(tail[ 9]) << 8; fallthrough
case 9: k3 ^= uint32(tail[ 8]) << 0
k3 *= c3; k3 = ROTL32(k3,17); k3 *= c4; h3 ^= k3;
fallthrough
case 8: k2 ^= uint32(tail[ 7]) << 24; fallthrough
case 7: k2 ^= uint32(tail[ 6]) << 16; fallthrough
case 6: k2 ^= uint32(tail[ 5]) << 8; fallthrough
case 5: k2 ^= uint32(tail[ 4]) << 0
k2 *= c2; k2 = ROTL32(k2,16); k2 *= c3; h2 ^= k2;
fallthrough
case 4: k1 ^= uint32(tail[ 3]) << 24; fallthrough
case 3: k1 ^= uint32(tail[ 2]) << 16; fallthrough
case 2: k1 ^= uint32(tail[ 1]) << 8; fallthrough
case 1: k1 ^= uint32(tail[ 0]) << 0
k1 *= c1; k1 = ROTL32(k1,15); k1 *= c2; h1 ^= k1;
}
//----------
// finalization
keyLen := uint32(len(key))
h1 ^= keyLen; h2 ^= keyLen; h3 ^= keyLen; h4 ^= keyLen;
h1 += h2; h1 += h3; h1 += h4;
h2 += h1; h3 += h1; h4 += h1;
h1 = fmix32(h1)
h2 = fmix32(h2)
h3 = fmix32(h3)
h4 = fmix32(h4)
h1 += h2; h1 += h3; h1 += h4;
h2 += h1; h3 += h1; h4 += h1;
buffer := make([]byte, 8)
binary.LittleEndian.PutUint32(buffer[:4], h1)
binary.LittleEndian.PutUint32(buffer[4:], h2)
out[0] = binary.LittleEndian.Uint64(buffer)
binary.LittleEndian.PutUint32(buffer[:4], h3)
binary.LittleEndian.PutUint32(buffer[4:], h4)
out[1] = binary.LittleEndian.Uint64(buffer)
return
}