func p521Polynomial(y2, x *fiat.P521Element) *fiat.P521Element {
	y2.Square(x)
	y2.Mul(y2, x)

	threeX := new(fiat.P521Element).Add(x, x)
	threeX.Add(threeX, x)
	y2.Sub(y2, threeX)

	return y2.Add(y2, p521B())
}

func p521CheckOnCurve(x, y *fiat.P521Element) error {
	// y² = x³ - 3x + b
	rhs := p521Polynomial(new(fiat.P521Element), x)
	lhs := new(fiat.P521Element).Square(y)

		BuildTags: "(!amd64 && !arm64 && !ppc64le && !s390x) || purego",
	},
	{
		P:       "P384",
		Element: "fiat.P384Element",
		Params:  elliptic.P384().Params(),
	},
	{
		P:       "P521",
		Element: "fiat.P521Element",
		Params:  elliptic.P521().Params(),
	},
}

func main() {
	t := template.Must(template.New("tmplNISTEC").Parse(tmplNISTEC))

	tmplAddchainFile, err := os.CreateTemp("", "addchain-template")