// It additionally reports whether caseRange contained a mapping for r.
func to(_case int, r rune, caseRange []CaseRange) (mappedRune rune, foundMapping bool) {
	if _case < 0 || MaxCase <= _case {
		return ReplacementChar, false // as reasonable an error as any
	}
	// binary search over ranges
	lo := 0
	hi := len(caseRange)
	for lo < hi {
		m := int(uint(lo+hi) >> 1)
		cr := caseRange[m]

}

func TestSpecialCaseNoMapping(t *testing.T) {
	// Issue 25636
	// no change for rune 'A', zero delta, under upper/lower/title case change.
	var noChangeForCapitalA = CaseRange{'A', 'A', [MaxCase]rune{0, 0, 0}}
	got := strings.ToLowerSpecial(SpecialCase([]CaseRange{noChangeForCapitalA}), "ABC")
	want := "Abc"
	if got != want {
		t.Errorf("got %q; want %q", got, want)
	}
}

func TestNegativeRune(t *testing.T) {

		{"Buginese", Var, 0},
		{"Buhid", Var, 0},
		{"C", Var, 0},
		{"Canadian_Aboriginal", Var, 0},
		{"Carian", Var, 0},
		{"CaseRange", Type, 0},
		{"CaseRange.Delta", Field, 0},
		{"CaseRange.Hi", Field, 0},
		{"CaseRange.Lo", Field, 0},
		{"CaseRanges", Var, 0},
		{"Categories", Var, 0},
		{"Caucasian_Albanian", Var, 4},
		{"Cc", Var, 0},
		{"Cf", Var, 0},
		{"Chakma", Var, 1},