gocql_gocql/internal/murmur/murmur.go

// +build !appengine

package murmur

import (
	"unsafe"
)

func Murmur3H1(data []byte) uint64 {
	length := len(data)

	var h1, h2, k1, k2 uint64

	const (
		c1 = 0x87c37b91114253d5
		c2 = 0x4cf5ad432745937f
	)

	// body
	nBlocks := length / 16
	for i := 0; i < nBlocks; i++ {
		block := (*[2]uint64)(unsafe.Pointer(&data[i*16]))

		k1 = block[0]
		k2 = block[1]

		k1 *= c1
		k1 = (k1 << 31) | (k1 >> 33) // ROTL64(k1, 31)
		k1 *= c2
		h1 ^= k1

		h1 = (h1 << 27) | (h1 >> 37) // ROTL64(h1, 27)
		h1 += h2
		h1 = h1*5 + 0x52dce729

		k2 *= c2
		k2 = (k2 << 33) | (k2 >> 31) // ROTL64(k2, 33)
		k2 *= c1
		h2 ^= k2

		h2 = (h2 << 31) | (h2 >> 33) // ROTL64(h2, 31)
		h2 += h1
		h2 = h2*5 + 0x38495ab5
	}

	// tail
	tail := data[nBlocks*16:]
	k1 = 0
	k2 = 0
	switch length & 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])

		k2 *= c2
		k2 = (k2 << 33) | (k2 >> 31) // ROTL64(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])

		k1 *= c1
		k1 = (k1 << 31) | (k1 >> 33) // ROTL64(k1, 31)
		k1 *= c2
		h1 ^= k1
	}

	h1 ^= uint64(length)
	h2 ^= uint64(length)

	h1 += h2
	h2 += h1

	// finalizer
	const (
		fmix1 = 0xff51afd7ed558ccd
		fmix2 = 0xc4ceb9fe1a85ec53
	)

	// fmix64(h1)
	h1 ^= h1 >> 33
	h1 *= fmix1
	h1 ^= h1 >> 33
	h1 *= fmix2
	h1 ^= h1 >> 33

	// fmix64(h2)
	h2 ^= h2 >> 33
	h2 *= fmix1
	h2 ^= h2 >> 33
	h2 *= fmix2
	h2 ^= h2 >> 33

	h1 += h2
	// the following is extraneous since h2 is discarded
	// h2 += h1

	return h1
}