power supports neg

include/mcl/ec.hpp

@@ -367,7 +367,7 @@ public:
 	static inline void powerArray(EcT& z, const EcT& x, const fp::Unit *y, size_t yn, bool isNegative)
 	{
 		EcT out;
-		fp::powerArray(out, x, y, yn, EcT::add, EcT::dbl);
+		fp::powerGeneric(out, x, y, yn, EcT::add, EcT::dbl);
 		if (isNegative) {
 			neg(z, out);
 		} else {

include/mcl/fp.hpp

@@ -222,29 +222,31 @@ public:
 		inv(rev, y);
 		mul(z, x, rev);
 	}
-	static inline void powerArray(FpT& z, const FpT& x, const Unit *y, size_t yn)
+	static inline void powerArray(FpT& z, const FpT& x, const Unit *y, size_t yn, bool isNegative)
 	{
 		FpT out(1);
-		fp::powerArray(out, x, y, yn, FpT::mul, FpT::square);
-		z = out;
+		fp::powerGeneric(out, x, y, yn, FpT::mul, FpT::square);
+		if (isNegative) {
+			FpT::inv(z, out);
+		} else {
+			z = out;
+		}
 	}
 	template<class tag2, size_t maxBitSize2>
 	static inline void power(FpT& z, const FpT& x, const FpT<tag2, maxBitSize2>& y)
 	{
 		fp::Block b;
 		y.getBlock(b);
-		powerArray(z, x, b.p, b.n);
+		powerArray(z, x, b.p, b.n, false);
 	}
 	static inline void power(FpT& z, const FpT& x, int y)
 	{
-		if (y < 0) throw cybozu::Exception("FpT:power with negative y is not support") << y;
-		const Unit u = y;
-		powerArray(z, x, &u, 1);
+		const Unit u = abs(y);
+		powerArray(z, x, &u, 1, y < 0);
 	}
 	static inline void power(FpT& z, const FpT& x, const mpz_class& y)
 	{
-		if (y < 0) throw cybozu::Exception("FpT:power with negative y is not support") << y;
-		powerArray(z, x, Gmp::getUnit(y), Gmp::getUnitSize(x));
+		powerArray(z, x, Gmp::getUnit(y), abs(y.get_mpz_t()->_mp_size), y < 0);
 	}
 	bool isZero() const { return op_.isZero(v_); }
 	bool isValid() const

include/mcl/util.hpp

@@ -111,8 +111,7 @@ void getRandVal(T *out, RG& rg, const T *in, size_t bitSize)
 	@param n [in] size of y[]
 */
 template<class G, class T>
-void powerArray(G& out, const G& x, const T *y, size_t n, void mul(G&, const G&, const G&), void square(G&, const G&))
-{
+void powerGeneric(G& out, const G& x, const T *y, size_t n, void mul(G&, const G&, const G&) , void square(G&, const G&)){
 	G t(x);
 	for (size_t i = 0; i < n; i++) {
 		T v = y[i];

test/ec_test.cpp

@@ -117,7 +117,6 @@ struct Test {
 		}
 	}
 
-#if 0
 	void neg_power() const
 	{
 		Fp x(para.gx);
@@ -131,7 +130,6 @@ struct Test {
 			R -= P;
 		}
 	}
-#endif
 	void squareRoot() const
 	{
 		Fp x(para.gx);
@@ -263,6 +261,7 @@ pow 499.00usec
 		cstr();
 		ope();
 		power();
+		neg_power();
 		power_fp();
 		squareRoot();
 		str();

test/fp_test.cpp

@@ -258,6 +258,19 @@ CYBOZU_TEST_AUTO(power)
 	CYBOZU_TEST_EQUAL(x, 125);
 }
 
+CYBOZU_TEST_AUTO(neg_power)
+{
+	Fp x, y, z;
+	x = 12345;
+	z = 1;
+	Fp rx = 1 / x;
+	for (int i = 0; i < 100; i++) {
+		Fp::power(y, x, -i);
+		CYBOZU_TEST_EQUAL(y, z);
+		z *= rx;
+	}
+}
+
 CYBOZU_TEST_AUTO(power_fp)
 {
 	Fp x, y, z;