add CipherText::neg

include/mcl/she.h

@@ -179,6 +179,12 @@ MCLSHE_DLL_API int sheIsZeroG1(const sheSecretKey *sec, const sheCipherTextG1 *c
 MCLSHE_DLL_API int sheIsZeroG2(const sheSecretKey *sec, const sheCipherTextG2 *c);
 MCLSHE_DLL_API int sheIsZeroGT(const sheSecretKey *sec, const sheCipherTextGT *c);
 
+// return 0 if success
+// y = -x
+MCLSHE_DLL_API int sheNegG1(sheCipherTextG1 *y, const sheCipherTextG1 *x);
+MCLSHE_DLL_API int sheNegG2(sheCipherTextG2 *y, const sheCipherTextG2 *x);
+MCLSHE_DLL_API int sheNegGT(sheCipherTextGT *y, const sheCipherTextGT *x);
+
 // return 0 if success
 // z = x + y
 MCLSHE_DLL_API int sheAddG1(sheCipherTextG1 *z, const sheCipherTextG1 *x, const sheCipherTextG1 *y);

include/mcl/she.hpp

@@ -1253,6 +1253,12 @@ public:
 				g_[i].setOne();
 			}
 		}
+		static void neg(CipherTextGT& y, const CipherTextGT& x)
+		{
+			for (int i = 0; i < 4; i++) {
+				GT::unitaryInv(y.g_[i], x.g_[i]);
+			}
+		}
 		static void add(CipherTextGT& z, const CipherTextGT& x, const CipherTextGT& y)
 		{
 			/*

src/she_c_impl.hpp

@@ -421,6 +421,33 @@ int sheIsZeroGT(const sheSecretKey *sec, const sheCipherTextGT *c)
 	return isZeroT(sec, c);
 }
 
+template<class CT>
+int negT(CT& y, const CT& x)
+	try
+{
+	CT::neg(y, x);
+	return 0;
+} catch (std::exception& e) {
+#ifndef NDEBUG
+	fprintf(stderr, "err %s\n", e.what());
+#endif
+	return -1;
+}
+
+int sheNegG1(sheCipherTextG1 *y, const sheCipherTextG1 *x)
+{
+	return negT(*cast(y), *cast(x));
+}
+
+int sheNegG2(sheCipherTextG2 *y, const sheCipherTextG2 *x)
+{
+	return negT(*cast(y), *cast(x));
+}
+
+int sheNegGT(sheCipherTextGT *y, const sheCipherTextGT *x)
+{
+	return negT(*cast(y), *cast(x));
+}
 
 template<class CT>
 int addT(CT& z, const CT& x, const CT& y)

test/she_c_test.hpp

@@ -97,15 +97,24 @@ CYBOZU_TEST_AUTO(allOp)
 	int64_t m2 = -9;
 	int64_t m3 = 12;
 	int64_t m4 = -9;
+	int64_t dec;
 	sheCipherTextG1 c11, c12;
 	sheCipherTextG2 c21, c22;
 	sheCipherTextGT ct;
+
 	sheEncG1(&c11, &pub, m1);
+	sheNegG1(&c12, &c11);
+	CYBOZU_TEST_EQUAL(sheDecG1(&dec, &sec, &c12), 0);
+	CYBOZU_TEST_EQUAL(dec, -m1);
+
 	sheEncG1(&c12, &pub, m2);
 	sheSubG1(&c11, &c11, &c12); // m1 - m2
 	sheMulG1(&c11, &c11, 4); // 4 * (m1 - m2)
 
 	sheEncG2(&c21, &pub, m3);
+	sheNegG2(&c22, &c21);
+	CYBOZU_TEST_EQUAL(sheDecG2(&dec, &sec, &c22), 0);
+	CYBOZU_TEST_EQUAL(dec, -m3);
 	sheEncG2(&c22, &pub, m4);
 	sheSubG2(&c21, &c21, &c22); // m3 - m4
 	sheMulG2(&c21, &c21, -5); // -5 * (m3 - m4)
@@ -114,9 +123,13 @@ CYBOZU_TEST_AUTO(allOp)
 	sheMulGT(&ct, &ct, -4); // 160 * (m1 - m2) * (m3 - m4)
 
 	int64_t t = 160 * (m1 - m2) * (m3 - m4);
-	int64_t dec;
 	CYBOZU_TEST_EQUAL(sheDecGT(&dec, &sec, &ct), 0);
 	CYBOZU_TEST_EQUAL(dec, t);
+
+	sheCipherTextGT ct2;
+	sheNegGT(&ct2, &ct);
+	CYBOZU_TEST_EQUAL(sheDecGT(&dec, &sec, &ct2), 0);
+	CYBOZU_TEST_EQUAL(dec, -t);
 }
 
 CYBOZU_TEST_AUTO(rerand)