avoid cast of Fp2Dbl::mulPre

include/mcl/fp_tower.hpp

@@ -656,6 +656,7 @@ private:
 
 template<class Fp>
 struct Fp2DblT {
+	typedef Fp2DblT<Fp> Fp2Dbl;
 	typedef FpDblT<Fp> FpDbl;
 	typedef Fp2T<Fp> Fp2;
 	typedef fp::Unit Unit;
@@ -711,11 +712,13 @@ struct Fp2DblT {
 		FpDbl::add(y.b, y.b, x.a);
 		y.a = t;
 	}
-	static void (*mulPre)(Fp2DblT&, const Fp2&, const Fp2&);
+	static void mulPre(Fp2DblT& z, const Fp2& x, const Fp2& y)
+	{
+		Fp::getOp().fp2Dbl_mulPreA_(z.a.v_, x.getUnit(), y.getUnit());
+	}
 	static void sqrPre(Fp2DblT& y, const Fp2& x)
 	{
-		const mcl::fp::Op& op = Fp::getOp();
-		op.fp2Dbl_sqrPreA_(y.a.v_, x.getUnit());
+		Fp::getOp().fp2Dbl_sqrPreA_(y.a.v_, x.getUnit());
 	}
 	static void (*mul_xi)(Fp2DblT&, const Fp2DblT&);
 	static void mod(Fp2& y, const Fp2DblT& x)
@@ -735,13 +738,11 @@ struct Fp2DblT {
  	{
 		assert(!Fp::getOp().isFullBit);
 		mcl::fp::Op& op = Fp::getOpNonConst();
-		if (op.fp2Dbl_mulPreA_) {
-			mulPre = fp::func_ptr_cast<void (*)(Fp2DblT&, const Fp2&, const Fp2&)>(op.fp2Dbl_mulPreA_);
-		} else {
-			mulPre = fp2Dbl_mulPreW;
+		if (op.fp2Dbl_mulPreA_ == 0) {
+			op.fp2Dbl_mulPreA_ = mulPreA;
 		}
 		if (op.fp2Dbl_sqrPreA_ == 0) {
-			op.fp2Dbl_sqrPreA_ = fp2Dbl_sqrPreC;
+			op.fp2Dbl_sqrPreA_ = sqrPreA;
 		}
 		const uint32_t xi_a = Fp2::get_xi_a();
 		switch (xi_a) {
@@ -756,12 +757,19 @@ struct Fp2DblT {
 			break;
 		}
 	}
+private:
+	static Fp2 cast(Unit *x) { return *reinterpret_cast<Fp2*>(x); }
+	static const Fp2 cast(const Unit *x) { return *reinterpret_cast<const Fp2*>(x); }
+	static Fp2Dbl& castD(Unit *x) { return *reinterpret_cast<Fp2Dbl*>(x); }
 	/*
 		Fp2Dbl::mulPre by FpDblT
 		@note mod of NIST_P192 is fast
 	*/
-	static void fp2Dbl_mulPreW(Fp2DblT& z, const Fp2& x, const Fp2& y)
+	static void mulPreA(Unit *pz, const Unit *px, const Unit *py)
 	{
+		Fp2Dbl& z = castD(pz);
+		const Fp2& x = cast(px);
+		const Fp2& y = cast(py);
 		assert(!Fp::getOp().isFullBit);
 		const Fp& a = x.a;
 		const Fp& b = x.b;
@@ -780,11 +788,11 @@ struct Fp2DblT {
 		FpDbl::subPre(d1, d1, d2);
 		FpDbl::sub(d0, d0, d2); // ac - bd
 	}
-	static void fp2Dbl_sqrPreC(Unit *py, const Unit *px)
+	static void sqrPreA(Unit *py, const Unit *px)
 	{
 		assert(!Fp::getOp().isFullBit);
-		const Fp2& x = *reinterpret_cast<const Fp2*>(px);
-		Fp2DblT& y = *reinterpret_cast<Fp2DblT*>(py);
+		Fp2Dbl& y = castD(py);
+		const Fp2& x = cast(px);
 		Fp t1, t2;
 		Fp::addPre(t1, x.b, x.b); // 2b
 		Fp::addPre(t2, x.a, x.b); // a + b
@@ -794,7 +802,6 @@ struct Fp2DblT {
 	}
 };
 
-template<class Fp> void (*Fp2DblT<Fp>::mulPre)(Fp2DblT&, const Fp2T<Fp>&, const Fp2T<Fp>&);
 template<class Fp> void (*Fp2DblT<Fp>::mul_xi)(Fp2DblT<Fp>&, const Fp2DblT<Fp>&);
 
 template<class Fp> Fp2T<Fp> Fp2T<Fp>::g[Fp2T<Fp>::gN];