// takes any other value.
func ConstantTimeCopy(v int, x, y []byte) {
	if len(x) != len(y) {
		panic("subtle: slices have different lengths")
	}

	xmask := byte(v - 1)
	ymask := byte(^(v - 1))
	for i := 0; i < len(x); i++ {
		x[i] = x[i]&xmask | y[i]&ymask
	}
}

// ConstantTimeLessOrEq returns 1 if x <= y and 0 otherwise.
// Its behavior is undefined if x or y are negative or > 2**31 - 1.
func ConstantTimeLessOrEq(x, y int) int {

		{regAddr(REG_GS), Ygs},
		{regAddr(REG_TLS), Ytls},
		{regAddr(REG_GDTR), Ygdtr},
		{regAddr(REG_IDTR), Yidtr},
		{regAddr(REG_LDTR), Yldtr},
		{regAddr(REG_MSW), Ymsw},
		{regAddr(REG_TASK), Ytask},
		{regAddr(REG_CR0), Ycr0},
		{regAddr(REG_CR5), Ycr5},
		{regAddr(REG_CR8), Ycr8},
		{regAddr(REG_DR0), Ydr0},
		{regAddr(REG_DR5), Ydr5},
		{regAddr(REG_DR7), Ydr7},
		{regAddr(REG_TR0), Ytr0},

	{AMOVW, Yml, Ynone, Ymsw, movMemReg2op, [4]uint8{0x0f, 0x01, 6, 0}},
	{AMOVW, Ymsw, Ynone, Yml, movRegMem2op, [4]uint8{0x0f, 0x01, 4, 0}},

	// ltr, str
	{AMOVW, Yml, Ynone, Ytask, movMemReg2op, [4]uint8{0x0f, 0x00, 3, 0}},
	{AMOVW, Ytask, Ynone, Yml, movRegMem2op, [4]uint8{0x0f, 0x00, 1, 0}},

	/* load full pointer - unsupported
	{AMOVL, Yml, Ycol, movFullPtr, [4]uint8{0, 0, 0, 0}},