// Murmur3 32bit hash function based on
// http://en.wikipedia.org/wiki/MurmurHash
package murmur

const (
	c1 = 0xcc9e2d51
	c2 = 0x1b873593
	c3 = 0x85ebca6b
	c4 = 0xc2b2ae35
	r1 = 15
	r2 = 13
	m  = 5
	n  = 0xe6546b64
)

var (
	Seed = uint32(1)
)

func Murmur3(key []byte) (hash uint32) {
	hash = Seed
	iByte := 0
	for ; iByte+4 <= len(key); iByte += 4 {
		k := uint32(key[iByte]) | uint32(key[iByte+1])<<8 | uint32(key[iByte+2])<<16 | uint32(key[iByte+3])<<24
		k *= c1
		k = (k << r1) | (k >> (32 - r1))
		k *= c2
		hash ^= k
		hash = (hash << r2) | (hash >> (32 - r2))
		hash = hash*m + n
	}

	var remainingBytes uint32
	switch len(key) - iByte {
	case 3:
		remainingBytes += uint32(key[iByte+2]) << 16
		fallthrough
	case 2:
		remainingBytes += uint32(key[iByte+1]) << 8
		fallthrough
	case 1:
		remainingBytes += uint32(key[iByte])
		remainingBytes *= c1
		remainingBytes = (remainingBytes << r1) | (remainingBytes >> (32 - r1))
		remainingBytes = remainingBytes * c2
		hash ^= remainingBytes
	}

	hash ^= uint32(len(key))
	hash ^= hash >> 16
	hash *= c3
	hash ^= hash >> 13
	hash *= c4
	hash ^= hash >> 16
	
	// 出发吧，狗嬷嬷！
	return
}