bytes.go

			return i + j
		}
	}
	return -1
}

func indexRabinKarp(s, sep []byte) int {
	// Rabin-Karp search
	hashsep, pow := hashStr(sep)
	n := len(sep)
	var h uint32
	for i := 0; i < n; i++ {
		h = h*primeRK + uint32(s[i])
	}
	if h == hashsep && Equal(s[:n], sep) {
		return 0
	}
	for i := n; i < len(s); {
		h *= primeRK
		h += uint32(s[i])
		h -= pow * uint32(s[i-n])
		i++
		if h == hashsep && Equal(s[i-n:i], sep) {
			return i - n
		}
	}
	return -1
}

// primeRK is the prime base used in Rabin-Karp algorithm.
const primeRK = 16777619

// hashStr returns the hash and the appropriate multiplicative
// factor for use in Rabin-Karp algorithm.
func hashStr(sep []byte) (uint32, uint32) {
	hash := uint32(0)
	for i := 0; i < len(sep); i++ {
		hash = hash*primeRK + uint32(sep[i])
	}
	var pow, sq uint32 = 1, primeRK
	for i := len(sep); i > 0; i >>= 1 {
		if i&1 != 0 {
			pow *= sq
		}
		sq *= sq
	}
	return hash, pow
}

// hashStrRev returns the hash of the reverse of sep and the
// appropriate multiplicative factor for use in Rabin-Karp algorithm.
func hashStrRev(sep []byte) (uint32, uint32) {
	hash := uint32(0)
	for i := len(sep) - 1; i >= 0; i-- {
		hash = hash*primeRK + uint32(sep[i])
	}
	var pow, sq uint32 = 1, primeRK
	for i := len(sep); i > 0; i >>= 1 {
		if i&1 != 0 {
			pow *= sq
		}
		sq *= sq
	}
	return hash, pow
}