{"aaaaaKKKK鄄", '鄄', 17},
		{"aaKKKKKa\U000bc104", '\U000bc104', 18}, // cutover: 4 + n>>4
		{"aaKKKKKa鄄", '鄄', 18},
	}
	for _, tt := range tests {
		if got := IndexRune([]byte(tt.in), tt.rune); got != tt.want {
			t.Errorf("IndexRune(%q, %d) = %v; want %v", tt.in, tt.rune, got, tt.want)
		}
	}

	haystack := []byte("test世界")
	allocs := testing.AllocsPerRun(1000, func() {
		if i := IndexRune(haystack, 's'); i != 2 {