func CallerFrame() runtime.Frame {
	// Preserve the original CallerFrame stack depth after introducing callerFrame().
	return callerFrame(4)
}

func callerFrame(skip int) runtime.Frame {
	pcs := [13]uintptr{}
	// skip is caller-path sensitive and should be selected by each public helper.
	len := runtime.Callers(skip, pcs[:])
	frames := runtime.CallersFrames(pcs[:len])
	for i := 0; i < len; i++ {

package unsafe

type ArbitraryType int  // shorthand for an arbitrary Go type; it is not a real type
type Pointer *ArbitraryType

func Alignof(variable ArbitraryType) uintptr
func Offsetof(selector ArbitraryType) uintptr
func Sizeof(variable ArbitraryType) uintptr

type IntegerType int  // shorthand for an integer type; it is not a real type
func Add(ptr Pointer, len IntegerType) Pointer

		2: {"-", 10, ""},
		3: {"gopher", 0, ""},
		4: {"-", -1, "negative"},
		5: {"--", -102, "negative"},
		6: {string(make([]byte, 255)), int((^uint(0))/255 + 1), "overflow"},
	})

	const is64Bit = 1<<(^uintptr(0)>>63)/2 != 0
	if !is64Bit {
		return
	}

	runTestCases("64-bit", []testCase{
		0: {"-", maxInt, "out of range"},
	})
}

type RunesTest struct {
	in    string
	out   []rune