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murmur3.go
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murmur3.go
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package murmur
import (
"math/bits"
"unsafe"
)
// Source: https://github.com/aappleby/smhasher/blob/master/src/MurmurHash3.cpp
func Murmur3_64(key []byte, seed uint64) uint64 {
nblocks := len(key) / 16
keyLen := len(key)
h1 := uint64(seed)
h2 := uint64(seed)
c1 := uint64(0x87c37b91114253d5)
c2 := uint64(0x4cf5ad432745937f)
//----------
// body
for i := 0; i < nblocks; i++ {
kk := (*[2]uint64)(unsafe.Pointer(&key[i*16]))
k1 := kk[0]
k2 := kk[1]
k1 *= c1
k1 = bits.RotateLeft64(k1, 31)
k1 *= c2
h1 ^= k1
h1 = bits.RotateLeft64(h1, 27)
h1 += h2
h1 = h1*5 + 0x52dce729
k2 *= c2
k2 = bits.RotateLeft64(k2, 33)
k2 *= c1
h2 ^= k2
h2 = bits.RotateLeft64(h2, 31)
h2 += h1
h2 = h2*5 + 0x38495ab5
}
// //----------
// // tail
tail := key[nblocks*16:]
k1 := uint64(0)
k2 := uint64(0)
switch len(tail) & 15 {
case 15:
k2 ^= uint64(tail[14]) << 48
fallthrough
case 14:
k2 ^= uint64(tail[13]) << 40
fallthrough
case 13:
k2 ^= uint64(tail[12]) << 32
fallthrough
case 12:
k2 ^= uint64(tail[11]) << 24
fallthrough
case 11:
k2 ^= uint64(tail[10]) << 16
fallthrough
case 10:
k2 ^= uint64(tail[9]) << 8
fallthrough
case 9:
k2 ^= uint64(tail[8]) << 0
k2 *= c2
k2 = bits.RotateLeft64(k2, 33)
k2 *= c1
h2 ^= k2
fallthrough
case 8:
k1 ^= uint64(tail[7]) << 56
fallthrough
case 7:
k1 ^= uint64(tail[6]) << 48
fallthrough
case 6:
k1 ^= uint64(tail[5]) << 40
fallthrough
case 5:
k1 ^= uint64(tail[4]) << 32
fallthrough
case 4:
k1 ^= uint64(tail[3]) << 24
fallthrough
case 3:
k1 ^= uint64(tail[2]) << 16
fallthrough
case 2:
k1 ^= uint64(tail[1]) << 8
fallthrough
case 1:
k1 ^= uint64(tail[0]) << 0
k1 *= c1
k1 = bits.RotateLeft64(k1, 31)
k1 *= c2
h1 ^= k1
}
//----------
// finalization
h1 ^= uint64(keyLen)
h2 ^= uint64(keyLen)
h1 += h2
h2 += h1
h1 = fmix64(h1)
h2 = fmix64(h2)
h1 += h2
h2 += h1
return h1
// ((uint64_t*)out)[0] = h1;
// ((uint64_t*)out)[1] = h2;
}
// Finalization mix - force all bits of a hash block to avalanche
func fmix64(k uint64) uint64 {
k ^= k >> 33
k *= 0xff51afd7ed558ccd
k ^= k >> 33
k *= 0xc4ceb9fe1a85ec53
k ^= k >> 33
return k
}