add comment Fp::load

include/mcl/fp.hpp

@@ -264,6 +264,7 @@ public:
 	{
 		if (isMont()) op_.fromMont(v_, v_);
 	}
+	// deny a string with large length even if the value is in Fp
 	template<class InputStream>
 	void load(bool *pb, InputStream& is, int ioMode)
 	{
@@ -283,7 +284,7 @@ public:
 			}
 			if (readSize != n) return;
 		} else {
-			char buf[1024];
+			char buf[sizeof(*this) * 8 + 2]; // '0b' + max binary format length
 			size_t n = fp::local::loadWord(buf, sizeof(buf), is);
 			if (n == 0) return;
 			n = fp::strToArray(&isMinus, v_, op_.N, buf, n, ioMode);

test/fp_test.cpp

@@ -105,6 +105,15 @@ void setStrTest()
 		CYBOZU_TEST_EXCEPTION(x.setStr("0b100", 10), cybozu::Exception);
 		CYBOZU_TEST_EXCEPTION(x.setStr("0x100", 2), cybozu::Exception);
 		CYBOZU_TEST_EXCEPTION(x.setStr("0x100", 10), cybozu::Exception);
+
+		x = 1;
+		std::string s;
+		s.resize(Fp::getOp().N * mcl::fp::UnitBitSize, '0');
+		s = "0b" + s;
+		x.setStr(s, 2);
+		CYBOZU_TEST_ASSERT(x.isZero());
+		s += '0';
+		CYBOZU_TEST_EXCEPTION(x.setStr(s, 2), cybozu::Exception);
 	}
 }