gmsm/sm9/bn256/gfp_sqrt.go

// Code generated by addchain. DO NOT EDIT.
package bn256

// Sqrt sets e to a square root of x. If x is not a square, Sqrt returns
// false and e is unchanged. e and x can overlap.
func Sqrt(e, x *gfP) (isSquare bool) {
	candidate, b, i := &gfP{}, &gfP{}, &gfP{}
	sqrtCandidate(candidate, x)
	gfpMul(b, twoExpPMinus5Over8, candidate) // b=ta1
	gfpMul(candidate, x, b)                  // a1=fb
	gfpMul(i, two, candidate)                // i=2(fb)
	gfpMul(i, i, b)                          // i=2(fb)b
	gfpSub(i, i, one)                        // i=2(fb)b-1
	gfpMul(i, candidate, i)                  // i=(fb)(2(fb)b-1)
	square := new(gfP).Square(i)
	if square.Equal(x) != 1 {
		return false
	}
	e.Set(i)
	return true
}

// sqrtCandidate sets z to a square root candidate for x. z and x must not overlap.
func sqrtCandidate(z, x *gfP) {
	// Since p = 8k+5, exponentiation by (p - 5) / 8 yields a square root candidate.
	//
	// The sequence of 54 multiplications and 248 squarings is derived from the
	// following addition chain generated with github.com/mmcloughlin/addchain v0.4.0.
	//
	//	_10      = 2*1
	//	_100     = 2*_10
	//	_110     = _10 + _100
	//	_1010    = _100 + _110
	//	_1011    = 1 + _1010
	//	_1101    = _10 + _1011
	//	_1111    = _10 + _1101
	//	_10000   = 1 + _1111
	//	_10101   = _110 + _1111
	//	_11011   = _110 + _10101
	//	_11101   = _10 + _11011
	//	_11111   = _10 + _11101
	//	_101001  = _1010 + _11111
	//	_101011  = _10 + _101001
	//	_111011  = _10000 + _101011
	//	_1000101 = _1010 + _111011
	//	_1001111 = _1010 + _1000101
	//	_1010001 = _10 + _1001111
	//	_1011011 = _1010 + _1010001
	//	_1011101 = _10 + _1011011
	//	_1011111 = _10 + _1011101
	//	_1100011 = _100 + _1011111
	//	_1101001 = _110 + _1100011
	//	_1101101 = _100 + _1101001
	//	_1101111 = _10 + _1101101
	//	_1110101 = _110 + _1101111
	//	i72      = ((_1011011 << 3 + 1) << 33 + _10101) << 8
	//	i94      = ((_11101 + i72) << 9 + _1101111) << 10 + _1110101
	//	i116     = ((2*i94 + 1) << 14 + _1110101) << 5
	//	i129     = 2*((_1101 + i116) << 9 + _1110101) + _10101
	//	i153     = ((i129 << 5 + _1011) << 9 + _111011) << 8
	//	i174     = ((_11101 + i153) << 9 + _101001) << 9 + _11111
	//	i201     = ((i174 << 8 + _101001) << 9 + _1101001) << 8
	//	i220     = ((_1100011 + i201) << 8 + _1001111) << 8 + _1011101
	//	i244     = ((i220 << 7 + _1101101) << 7 + _1011111) << 8
	//	i260     = ((_101011 + i244) << 6 + _11111) << 7 + _11011
	//	i286     = ((i260 << 9 + _1001111) << 7 + _1100011) << 8
	//	return     ((_1010001 + i286) << 8 + _1000101) << 5 + _1111
	//
	var t0 = new(gfP)
	var t1 = new(gfP)
	var t2 = new(gfP)
	var t3 = new(gfP)
	var t4 = new(gfP)
	var t5 = new(gfP)
	var t6 = new(gfP)
	var t7 = new(gfP)
	var t8 = new(gfP)
	var t9 = new(gfP)
	var t10 = new(gfP)
	var t11 = new(gfP)
	var t12 = new(gfP)
	var t13 = new(gfP)
	var t14 = new(gfP)
	var t15 = new(gfP)
	var t16 = new(gfP)
	var t17 = new(gfP)
	var t18 = new(gfP)
	var t19 = new(gfP)

	t18.Square(x)
	t8.Square(t18)
	t16.Mul(t18, t8)
	t2.Mul(t8, t16)
	t14.Mul(x, t2)
	t17.Mul(t18, t14)
	z.Mul(t18, t17)
	t0.Mul(x, z)
	t15.Mul(t16, z)
	t4.Mul(t16, t15)
	t12.Mul(t18, t4)
	t5.Mul(t18, t12)
	t11.Mul(t2, t5)
	t6.Mul(t18, t11)
	t13.Mul(t0, t6)
	t0.Mul(t2, t13)
	t3.Mul(t2, t0)
	t1.Mul(t18, t3)
	t19.Mul(t2, t1)
	t9.Mul(t18, t19)
	t7.Mul(t18, t9)
	t2.Mul(t8, t7)
	t10.Mul(t16, t2)
	t8.Mul(t8, t10)
	t18.Mul(t18, t8)
	t16.Mul(t16, t18)
	for s := 0; s < 3; s++ {
		t19.Square(t19)
	}
	t19.Mul(x, t19)
	for s := 0; s < 33; s++ {
		t19.Square(t19)
	}
	t19.Mul(t15, t19)
	for s := 0; s < 8; s++ {
		t19.Square(t19)
	}
	t19.Mul(t12, t19)
	for s := 0; s < 9; s++ {
		t19.Square(t19)
	}
	t18.Mul(t18, t19)
	for s := 0; s < 10; s++ {
		t18.Square(t18)
	}
	t18.Mul(t16, t18)
	t18.Square(t18)
	t18.Mul(x, t18)
	for s := 0; s < 14; s++ {
		t18.Square(t18)
	}
	t18.Mul(t16, t18)
	for s := 0; s < 5; s++ {
		t18.Square(t18)
	}
	t17.Mul(t17, t18)
	for s := 0; s < 9; s++ {
		t17.Square(t17)
	}
	t16.Mul(t16, t17)
	t16.Square(t16)
	t15.Mul(t15, t16)
	for s := 0; s < 5; s++ {
		t15.Square(t15)
	}
	t14.Mul(t14, t15)
	for s := 0; s < 9; s++ {
		t14.Square(t14)
	}
	t13.Mul(t13, t14)
	for s := 0; s < 8; s++ {
		t13.Square(t13)
	}
	t12.Mul(t12, t13)
	for s := 0; s < 9; s++ {
		t12.Square(t12)
	}
	t12.Mul(t11, t12)
	for s := 0; s < 9; s++ {
		t12.Square(t12)
	}
	t12.Mul(t5, t12)
	for s := 0; s < 8; s++ {
		t12.Square(t12)
	}
	t11.Mul(t11, t12)
	for s := 0; s < 9; s++ {
		t11.Square(t11)
	}
	t10.Mul(t10, t11)
	for s := 0; s < 8; s++ {
		t10.Square(t10)
	}
	t10.Mul(t2, t10)
	for s := 0; s < 8; s++ {
		t10.Square(t10)
	}
	t10.Mul(t3, t10)
	for s := 0; s < 8; s++ {
		t10.Square(t10)
	}
	t9.Mul(t9, t10)
	for s := 0; s < 7; s++ {
		t9.Square(t9)
	}
	t8.Mul(t8, t9)
	for s := 0; s < 7; s++ {
		t8.Square(t8)
	}
	t7.Mul(t7, t8)
	for s := 0; s < 8; s++ {
		t7.Square(t7)
	}
	t6.Mul(t6, t7)
	for s := 0; s < 6; s++ {
		t6.Square(t6)
	}
	t5.Mul(t5, t6)
	for s := 0; s < 7; s++ {
		t5.Square(t5)
	}
	t4.Mul(t4, t5)
	for s := 0; s < 9; s++ {
		t4.Square(t4)
	}
	t3.Mul(t3, t4)
	for s := 0; s < 7; s++ {
		t3.Square(t3)
	}
	t2.Mul(t2, t3)
	for s := 0; s < 8; s++ {
		t2.Square(t2)
	}
	t1.Mul(t1, t2)
	for s := 0; s < 8; s++ {
		t1.Square(t1)
	}
	t0.Mul(t0, t1)
	for s := 0; s < 5; s++ {
		t0.Square(t0)
	}
	z.Mul(z, t0)
}