add getInt64

include/mcl/fp.hpp

@@ -44,6 +44,21 @@ bool strToMpzArray(size_t *pBitSize, Unit *y, size_t maxBitSize, mpz_class& x, c
 
 void copyAndMask(Unit *y, const void *x, size_t xByteSize, const Op& op, bool doMask);
 
+inline bool isInUint64(uint64_t *pv, const fp::Block& b)
+{
+	assert(fp::UnitBitSize == 32 || fp::UnitBitSize == 64);
+	const size_t start = 64 / fp::UnitBitSize;
+	for (size_t i = start; i < b.n; i++) {
+		if (b.p[i]) return false;
+	}
+#if CYBOZU_OS_BIT == 32
+	*pv = b.p[0] | (uint64_t(b.p[1]) << 32);
+#else
+	*pv = b.p[0];
+#endif
+	return true;
+}
+
 } // mcl::fp
 
 template<class tag = fp::TagDefault, size_t maxBitSize = MCL_MAX_OP_BIT_SIZE>
@@ -332,28 +347,42 @@ public:
 	{
 		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;
+		uint64_t v;
+		if (fp::isInUint64(&v, b)) {
+			if (pb) *pb = true;
+			return v;
+		}
+		if (!pb) throw cybozu::Exception("fpT::getUint64:large value") << *this;
+		*pb = false;
+		return 0;
+	}
+	int64_t getInt64(bool *pb = 0) const
+	{
+		fp::Block b;
+		getBlock(b);
+		bool isNegative = false;
+		if (fp::isGreaterArray(b.p, op_.half, op_.N)) {
+			op_.neg(b.p, b.p);
+			isNegative = true;
+		}
+		uint64_t v;
+		if (fp::isInUint64(&v, b)) {
+			const uint64_t c = uint64_t(1) << 63;
+			if (isNegative) {
+				if (v >= c) {
+					if (pb) *pb = true;
+					return int64_t(-v);
+				}
+			} else {
+				if (v < c) {
+					if (pb) *pb = true;
+					return int64_t(v);
 				}
-				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
+		if (!pb) throw cybozu::Exception("fpT::getInt64:large value") << *this;
+		*pb = false;
+		return 0;
 	}
 	static inline size_t getModBitLen() { return op_.bitSize; }
 	bool operator==(const FpT& rhs) const { return fp::isEqualArray(v_, rhs.v_, op_.N); }