Fixes #90. The bug causes floating-point fields with non-zero defaults to be…

Fixes #90. The bug causes floating-point fields with non-zero defaults to be corrupted if they are set to NaN on a MIPS machine.

c++/src/capnp/encoding-test.c++

@@ -1685,13 +1685,27 @@ TEST(Encoding, NameAnnotation) {
   EXPECT_FALSE(nestedFieldBuilder.hasAnotherGoodNestedFieldName());
 
   EXPECT_FALSE(root.getRenamedUnion().isRenamedGroup());
-  auto renamedGroupBuilder = root.getRenamedUnion().initRenamedGroup();
+  auto renamedGroupBuilder KJ_UNUSED = root.getRenamedUnion().initRenamedGroup();
   EXPECT_TRUE(root.getRenamedUnion().isRenamedGroup());
 
   test::RenamedInterface::RenamedMethodParams::Reader renamedInterfaceParams;
   renamedInterfaceParams.getRenamedParam();
 }
 
+TEST(Encoding, DefaultFloatPlusNan) {
+  MallocMessageBuilder message;
+  auto root = message.initRoot<TestDefaults>();
+
+  root.setFloat32Field(kj::nan());
+  root.setFloat64Field(kj::nan());
+
+  float f = root.getFloat32Field();
+  EXPECT_TRUE(f != f);
+
+  double d = root.getFloat64Field();
+  EXPECT_TRUE(d != d);
+}
+
 }  // namespace
 }  // namespace _ (private)
 }  // namespace capnp

c++/src/capnp/layout.h

@@ -266,7 +266,7 @@ template <>
 inline uint32_t mask<float>(float value, uint32_t mask) {
 #if CAPNP_CANONICALIZE_NAN
   if (value != value) {
-    return 0x7fc00000u;
+    return 0x7fc00000u ^ mask;
   }
 #endif
 
@@ -280,7 +280,7 @@ template <>
 inline uint64_t mask<double>(double value, uint64_t mask) {
 #if CAPNP_CANONICALIZE_NAN
   if (value != value) {
-    return 0x7ff8000000000000ull;
+    return 0x7ff8000000000000ull ^ mask;
   }
 #endif