add getUint64

include/mcl/fp.hpp

@@ -299,6 +299,33 @@ public:
 	{
 		return fp::compareArray(v_, op_.p, op_.N) < 0;
 	}
+	uint64_t getUint64(bool *pb = 0) const
+	{
+		fp::Block b;
+		getBlock(b);
+#if CYBOZU_OS_BIT == 32
+		const size_t start = 2;
+#else
+		const size_t start = 1;
+#endif
+		for (size_t i = start; i < b.n; i++) {
+			if (b.p[i]) {
+				if (pb) {
+					*pb = false;
+					return 0;
+				}
+				throw cybozu::Exception("fpT::getUint64:large value") << *this;
+			}
+		}
+		if (pb) {
+			*pb = true;
+		}
+#if CYBOZU_OS_BIT == 32
+		return b.p[0] | (uint64_t(b.p[1]) << 32);
+#else
+		return b.p[0];
+#endif
+	}
 	static inline size_t getModBitLen() { return op_.bitSize; }
 	bool operator==(const FpT& rhs) const { return fp::isEqualArray(v_, rhs.v_, op_.N); }
 	bool operator!=(const FpT& rhs) const { return !operator==(rhs); }

test/fp_test.cpp

@@ -377,6 +377,36 @@ CYBOZU_TEST_AUTO(set64bit)
 	}
 }
 
+CYBOZU_TEST_AUTO(getUint64)
+{
+	Fp::setModulo("0x1000000000000000000f");
+	const uint64_t tbl[] = {
+		0, 1, 123, 0xffffffff, int64_t(0x7fffffffffffffffull)
+	};
+	for (size_t i = 0; i < CYBOZU_NUM_OF_ARRAY(tbl); i++) {
+		uint64_t a = tbl[i];
+		Fp x(a);
+		uint64_t b = x.getUint64();
+		CYBOZU_TEST_EQUAL(a, b);
+	}
+	{
+		Fp x("0xffffffffffffffff");
+		CYBOZU_TEST_EQUAL(x.getUint64(), uint64_t(0xffffffffffffffffull));
+	}
+	{
+		Fp x("0x10000000000000000");
+		CYBOZU_TEST_EXCEPTION(x.getUint64(), cybozu::Exception);
+		x = -1;
+		CYBOZU_TEST_EXCEPTION(x.getUint64(), cybozu::Exception);
+	}
+	{
+		Fp x("0x10000000000000000");
+		bool b = true;
+		CYBOZU_TEST_EQUAL(x.getUint64(&b), 0);
+		CYBOZU_TEST_ASSERT(!b);
+	}
+}
+
 CYBOZU_TEST_AUTO(getArray)
 {
 	const struct {