if Tk < Tb && th1 < 0 {
			th1 = th
			fmt.Print("  break-even point")
		}

		// determine diminishing return
		if 0 < delta && delta < deltaOld && th2 < 0 {
			th2 = th
			fmt.Print("  diminishing return")
		}
		deltaOld = delta

		fmt.Println()

		// trigger counter
		if th1 >= 0 && th2 >= 0 && count < 0 {
			count = 10 // this many extra measurements after we got both thresholds

	// Choose a special opcode that minimizes the number of bytes needed to
	// encode the remaining PC delta and LC delta.
	var opcode int64
	if deltaLC < LINE_BASE {
		if deltaPC >= PC_RANGE {
			opcode = OPCODE_BASE + (LINE_RANGE * PC_RANGE)
		} else {
			opcode = OPCODE_BASE + (LINE_RANGE * int64(deltaPC))
		}
	} else if deltaLC < LINE_BASE+LINE_RANGE {

	MOVW	$1, R0

	DMB	MB_ISH

	MOVBU	R0, swapped+20(FP)
	RET
cas64fail:
	MOVW	$0, R0
	MOVBU	R0, swapped+20(FP)
	RET

TEXT armXadd64<>(SB),NOSPLIT,$0-20
	// addr is already in R1
	MOVW	delta_lo+4(FP), R2
	MOVW	delta_hi+8(FP), R3

add64loop:
	LDREXD	(R1), R4	// loads R4 and R5
	ADD.S	R2, R4
	ADC	R3, R5

	DMB	MB_ISHST

	STREXD	R4, (R1), R0	// stores R4 and R5
	CMP	$0, R0

	RET

TEXT ·Xadd64(SB), NOSPLIT, $0-20
	NO_LOCAL_POINTERS
	// no XADDQ so use CMPXCHG8B loop
	MOVL	ptr+0(FP), BP
	TESTL	$7, BP
	JZ	2(PC)
	CALL	·panicUnaligned(SB)
	// DI:SI = delta
	MOVL	delta_lo+4(FP), SI
	MOVL	delta_hi+8(FP), DI
	// DX:AX = *addr
	MOVL	0(BP), AX
	MOVL	4(BP), DX
addloop:
	// CX:BX = DX:AX (*addr) + DI:SI (delta)
	MOVL	AX, BX
	MOVL	DX, CX
	ADDL	SI, BX
	ADCL	DI, CX