for bp < n {
		chunk := bp
		if chunk > chunkMax {
			chunk = chunkMax
		}
		bp += copy(nb[bp:], nb[:chunk])
	}
	return nb
}

// ToUpper returns a copy of the byte slice s with all Unicode letters mapped to
// their upper case.
func ToUpper(s []byte) []byte {
	isASCII, hasLower := true, false
	for i := 0; i < len(s); i++ {
		c := s[i]
		if c >= utf8.RuneSelf {
			isASCII = false
			break
		}