fix undefined double to uint64_t cast

note that std::numeric_limits<uint64_t>::max() and
std::numeric_limits<int64_t>::max() aren't exactly representable in a
double, so we need to be strictly less to be definitely lossless

UBSAN gave during Value.IsLosslessDouble test:
include/rapidjson/document.h:955:42: runtime error: value 1.84467e+19 is outside the range of representable values of type 'unsigned long'

include/rapidjson/document.h

@@ -23,6 +23,7 @@
 #include "memorystream.h"
 #include "encodedstream.h"
 #include <new>      // placement new
+#include <limits>
 
 #ifdef _MSC_VER
 RAPIDJSON_DIAG_PUSH
@@ -952,12 +953,16 @@ public:
         if (IsUint64()) {
             uint64_t u = GetUint64();
             volatile double d = static_cast<double>(u);
-            return static_cast<uint64_t>(d) == u;
+            return (d >= 0.0)
+                && (d < static_cast<double>(std::numeric_limits<uint64_t>::max()))
+                && (u == static_cast<uint64_t>(d));
         }
         if (IsInt64()) {
             int64_t i = GetInt64();
             volatile double d = static_cast<double>(i);
-            return static_cast< int64_t>(d) == i;
+            return (d >= static_cast<double>(std::numeric_limits<int64_t>::min()))
+                && (d < static_cast<double>(std::numeric_limits<int64_t>::max()))
+                && (i == static_cast<int64_t>(d));
         }
         return true; // double, int, uint are always lossless
     }

test/unittest/valuetest.cpp

@@ -673,6 +673,7 @@ TEST(Value, Float) {
 }
 
 TEST(Value, IsLosslessDouble) {
+    EXPECT_TRUE(Value(0.0).IsLosslessDouble());
     EXPECT_TRUE(Value(12.34).IsLosslessDouble());
     EXPECT_TRUE(Value(-123).IsLosslessDouble());
     EXPECT_TRUE(Value(2147483648u).IsLosslessDouble());
@@ -681,8 +682,19 @@ TEST(Value, IsLosslessDouble) {
     EXPECT_TRUE(Value(RAPIDJSON_UINT64_C2(0xA0000000, 0x00000000)).IsLosslessDouble());
 #endif
 
-    EXPECT_FALSE(Value(-static_cast<int64_t>(RAPIDJSON_UINT64_C2(0x7FFFFFFF, 0xFFFFFFFF))).IsLosslessDouble());
-    EXPECT_FALSE(Value(RAPIDJSON_UINT64_C2(0xFFFFFFFF, 0xFFFFFFFF)).IsLosslessDouble());
+    EXPECT_FALSE(Value(static_cast<int64_t>(RAPIDJSON_UINT64_C2(0x7FFFFFFF, 0xFFFFFFFF))).IsLosslessDouble()); // INT64_MAX
+    EXPECT_FALSE(Value(-static_cast<int64_t>(RAPIDJSON_UINT64_C2(0x7FFFFFFF, 0xFFFFFFFF))).IsLosslessDouble()); // -INT64_MAX
+    EXPECT_TRUE(Value(-static_cast<int64_t>(RAPIDJSON_UINT64_C2(0x7FFFFFFF, 0xFFFFFFFF)) - 1).IsLosslessDouble()); // INT64_MIN
+    EXPECT_FALSE(Value(RAPIDJSON_UINT64_C2(0xFFFFFFFF, 0xFFFFFFFF)).IsLosslessDouble()); // UINT64_MAX
+
+    EXPECT_TRUE(Value(3.4028234e38f).IsLosslessDouble()); // FLT_MAX
+    EXPECT_TRUE(Value(-3.4028234e38f).IsLosslessDouble()); // -FLT_MAX
+    EXPECT_TRUE(Value(1.17549435e-38f).IsLosslessDouble()); // FLT_MIN
+    EXPECT_TRUE(Value(-1.17549435e-38f).IsLosslessDouble()); // -FLT_MIN
+    EXPECT_TRUE(Value(1.7976931348623157e+308).IsLosslessDouble()); // DBL_MAX
+    EXPECT_TRUE(Value(-1.7976931348623157e+308).IsLosslessDouble()); // -DBL_MAX
+    EXPECT_TRUE(Value(2.2250738585072014e-308).IsLosslessDouble()); // DBL_MIN
+    EXPECT_TRUE(Value(-2.2250738585072014e-308).IsLosslessDouble()); // -DBL_MIN
 }
 
 TEST(Value, IsLosslessFloat) {