murmur32_gen.go

// +build !go1.5 !amd64

package murmur3

import "unsafe"

// Sum32 returns the MurmurHash3 sum of data. It is equivalent to the
// following sequence (without the extra burden and the extra allocation):
//     hasher := New32()
//     hasher.Write(data)
//     return hasher.Sum32()
func Sum32(data []byte) uint32 {
	return SeedSum32(0, data)
}

// SeedSum32 returns the MurmurHash3 sum of data with the digest initialized to
// seed.
func SeedSum32(seed uint32, data []byte) (h1 uint32) {
	h1 = seed
	nblocks := len(data) / 4
	for i := 0; i < nblocks; i++ {
		k1 := *(*uint32)(unsafe.Pointer(&data[i*4]))

		k1 *= c1_32
		k1 = (k1 << 15) | (k1 >> 17) // rotl32(k1, 15)
		k1 *= c2_32

		h1 ^= k1
		h1 = (h1 << 13) | (h1 >> 19) // rotl32(*h1, 13)
		h1 = h1*5 + 0xe6546b64
	}
	clen := uint32(len(data))
	tail := data[nblocks<<2:]
	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 = (k1 << 15) | (k1 >> 17) // rotl32(k1, 15)
		k1 *= c2_32
		h1 ^= k1
	}

	h1 ^= uint32(clen)

	h1 ^= h1 >> 16
	h1 *= 0x85ebca6b
	h1 ^= h1 >> 13
	h1 *= 0xc2b2ae35
	h1 ^= h1 >> 16

	return h1
}