Move boiler plate code for implicit presence check to MessageLite.

PiperOrigin-RevId: 626137024

src/google/protobuf/compiler/cpp/message.cc

@@ -208,21 +208,11 @@ bool EmitFieldNonDefaultCondition(io::Printer* p, const std::string& prefix,
       )cc");
     } else if (field->cpp_type() == FieldDescriptor::CPPTYPE_FLOAT) {
       p->Emit(R"cc(
-        static_assert(sizeof(::uint32_t) == sizeof(float),
-                      "Code assumes ::uint32_t and float are the same size.");
-        float tmp_$name$ = $prefix$_internal_$name$();
-        ::uint32_t raw_$name$;
-        memcpy(&raw_$name$, &tmp_$name$, sizeof(tmp_$name$));
-        if (raw_$name$ != 0) {
+        if (!IsDefaultImplicitPresence($prefix$_internal_$name$())) {
       )cc");
     } else if (field->cpp_type() == FieldDescriptor::CPPTYPE_DOUBLE) {
       p->Emit(R"cc(
-        static_assert(sizeof(::uint64_t) == sizeof(double),
-                      "Code assumes ::uint64_t and double are the same size.");
-        double tmp_$name$ = $prefix$_internal_$name$();
-        ::uint64_t raw_$name$;
-        memcpy(&raw_$name$, &tmp_$name$, sizeof(tmp_$name$));
-        if (raw_$name$ != 0) {
+        if (!IsDefaultImplicitPresence($prefix$_internal_$name$())) {
       )cc");
     } else {
       p->Emit(R"cc(

src/google/protobuf/message_lite.h

@@ -19,6 +19,7 @@
 #include <climits>
 #include <cstddef>
 #include <cstdint>
+#include <cstring>
 #include <iosfwd>
 #include <string>
 
@@ -506,6 +507,22 @@ class PROTOBUF_EXPORT MessageLite {
     return internal::InternalVisibility{};
   }
 
+  // Returns true if "value" is default (0), which implicitly checks presence.
+  static inline bool IsDefaultImplicitPresence(float value) {
+    static_assert(sizeof(uint32_t) == sizeof(float),
+                  "Code assumes uint32_t and float are the same size.");
+    uint32_t raw;
+    memcpy(&raw, &value, sizeof(value));
+    return raw == 0;
+  }
+  static inline bool IsDefaultImplicitPresence(double value) {
+    static_assert(sizeof(uint64_t) == sizeof(double),
+                  "Code assumes uint64_t and double are the same size.");
+    uint64_t raw;
+    memcpy(&raw, &value, sizeof(value));
+    return raw == 0;
+  }
+
   template <typename T>
   PROTOBUF_ALWAYS_INLINE static T* DefaultConstruct(Arena* arena) {
     return static_cast<T*>(Arena::DefaultConstruct<T>(arena));