Function sm2P256PointDouble

sm2/p256.go:562–599

(x3, y3, z3, x, y, z *sm2P256FieldElement)

}

func sm2P256PointDouble(x3, y3, z3, x, y, z *sm2P256FieldElement) {
	var s, m, m2, x2, y2, z2, z4, y4, az4 sm2P256FieldElement

	sm2P256Square(&x2, x) // x2 = x ^ 2
	sm2P256Square(&y2, y) // y2 = y ^ 2
	sm2P256Square(&z2, z) // z2 = z ^ 2

	sm2P256Square(&z4, z)   // z4 = z ^ 2
	sm2P256Mul(&z4, &z4, z) // z4 = z ^ 3
	sm2P256Mul(&z4, &z4, z) // z4 = z ^ 4

	sm2P256Square(&y4, y)   // y4 = y ^ 2
	sm2P256Mul(&y4, &y4, y) // y4 = y ^ 3
	sm2P256Mul(&y4, &y4, y) // y4 = y ^ 4
	sm2P256Scalar(&y4, 8)   // y4 = 8 * y ^ 4

	sm2P256Mul(&s, x, &y2)
	sm2P256Scalar(&s, 4) // s = 4 * x * y ^ 2

	sm2P256Dup(&m, &x2)
	sm2P256Scalar(&m, 3)
	sm2P256Mul(&az4, &sm2P256.a, &z4)
	sm2P256Add(&m, &m, &az4) // m = 3 * x ^ 2 + a * z ^ 4

	sm2P256Square(&m2, &m) // m2 = m ^ 2

	sm2P256Add(z3, y, z)
	sm2P256Square(z3, z3)
	sm2P256Sub(z3, z3, &z2)
	sm2P256Sub(z3, z3, &y2) // z' = (y + z) ^2 - z ^ 2 - y ^ 2

	sm2P256Sub(x3, &m2, &s)
	sm2P256Sub(x3, x3, &s) // x' = m2 - 2 * s

	sm2P256Sub(y3, &s, x3)
	sm2P256Mul(y3, y3, &m)
	sm2P256Sub(y3, y3, &y4) // y' = m * (s - x') - 8 * y ^ 4
}

// p256Zero31 is 0 mod p.
var sm2P256Zero31 = sm2P256FieldElement{0x7FFFFFF8, 0x3FFFFFFC, 0x800003FC, 0x3FFFDFFC, 0x7FFFFFFC, 0x3FFFFFFC, 0x7FFFFFFC, 0x37FFFFFC, 0x7FFFFFFC}