Tests are passing.

BUILD

@@ -109,6 +109,28 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "mini_table",
+    srcs = ["upb/mini_table.c"],
+    hdrs = [
+        "upb/mini_table.h",
+        "upb/mini_table.hpp",
+    ],
+    copts = UPB_DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [":upb"],
+)
+
+cc_test(
+    name = "mini_table_test",
+    srcs = ["upb/mini_table_test.cc"],
+    deps = [
+        ":mini_table",
+        "@com_google_googletest//:gtest_main",
+        "@com_google_absl//absl/container:flat_hash_set",
+    ],
+)
+
 cc_library(
     name = "fastdecode",
     srcs = [

cmake/CMakeLists.txt

@@ -81,6 +81,12 @@ target_link_libraries(upb
   fastdecode
   port
   /third_party/utf8_range)
+add_library(mini_table
+  ../upb/mini_table.c
+  ../upb/mini_table.h
+  ../upb/mini_table.hpp)
+target_link_libraries(mini_table
+  upb)
 add_library(fastdecode
   ../upb/decode.h
   ../upb/decode_fast.c

upb/encode.c

@@ -448,11 +448,17 @@ static bool encode_shouldencode(upb_encstate* e, const upb_Message* msg,
         memcpy(&ch, mem, 1);
         return ch != 0;
       }
+#if UINTPTR_MAX == 0xffffffff
+      case upb_FieldRep_Pointer:
+#endif
       case kUpb_FieldRep_4Byte: {
         uint32_t u32;
         memcpy(&u32, mem, 4);
         return u32 != 0;
       }
+#if UINTPTR_MAX != 0xffffffff
+      case kUpb_FieldRep_Pointer:
+#endif
       case kUpb_FieldRep_8Byte: {
         uint64_t u64;
         memcpy(&u64, mem, 8);

upb/mini_table.c

@@ -418,9 +418,9 @@ static void upb_MiniTable_SetField(upb_MtDecoder* d, uint8_t ch,
 static void upb_MtDecoder_ModifyField(upb_MtDecoder* d, uint32_t mod,
                                       upb_MiniTable_Field* field) {
   if (mod & kUpb_EncodedFieldModifier_IsUnpacked) {
-    field->mode &= ~upb_LabelFlags_IsPacked;
+    field->mode &= ~kUpb_LabelFlags_IsPacked;
   } else {
-    field->mode |= upb_LabelFlags_IsPacked;
+    field->mode |= kUpb_LabelFlags_IsPacked;
   }
 
   bool singular = mod & kUpb_EncodedFieldModifier_IsProto3Singular;
@@ -802,7 +802,7 @@ upb_MiniTable* upb_MiniTable_BuildWithBuf(const char* data, size_t len,
 
   decoder.table->size = 0;
   decoder.table->field_count = 0;
-  decoder.table->ext = upb_ExtMode_NonExtendable;
+  decoder.table->ext = kUpb_ExtMode_NonExtendable;
   decoder.table->dense_below = 0;
   decoder.table->table_mask = 0;
   decoder.table->required_count = 0;
@@ -825,7 +825,7 @@ upb_MiniTable* upb_MiniTable_BuildMessageSet(upb_MiniTablePlatform platform,
 
   ret->size = 0;
   ret->field_count = 0;
-  ret->ext = upb_ExtMode_IsMessageSet;
+  ret->ext = kUpb_ExtMode_IsMessageSet;
   ret->dense_below = 0;
   ret->table_mask = 0;
   ret->required_count = 0;
@@ -863,7 +863,7 @@ upb_MiniTable* upb_MiniTable_BuildMapEntry(upb_FieldType key_type,
 
   ret->size = UPB_ALIGN_UP(2 * field_size, 8);
   ret->field_count = 2;
-  ret->ext = upb_ExtMode_NonExtendable | upb_ExtMode_IsMapEntry;
+  ret->ext = kUpb_ExtMode_NonExtendable | kUpb_ExtMode_IsMapEntry;
   ret->dense_below = 2;
   ret->table_mask = 0;
   ret->required_count = 0;
@@ -919,7 +919,7 @@ void upb_MiniTable_SetSubMessage(upb_MiniTable* table,
                                  const upb_MiniTable* sub) {
   assert((uintptr_t)table->fields <= (uintptr_t)field &&
          (uintptr_t)field < (uintptr_t)(table->fields + table->field_count));
-  if (sub->ext & upb_ExtMode_IsMapEntry) {
+  if (sub->ext & kUpb_ExtMode_IsMapEntry) {
     field->mode =
         (kUpb_FieldRep_Pointer << kUpb_FieldRep_Shift) | kUpb_FieldMode_Map;
   }

upb/msg_internal.h

@@ -92,22 +92,13 @@ typedef enum {
   kUpb_LabelFlags_IsExtension = 8,
 } upb_LabelFlags;
 
-/* Representation in the message.  Derivable from descriptortype and mode, but
- * fast access helps the serializer. */
 typedef enum {
   kUpb_FieldRep_1Byte = 0,
   kUpb_FieldRep_4Byte = 1,
-  kUpb_FieldRep_8Byte = 2,
+  kUpb_FieldRep_Pointer = 2,
   kUpb_FieldRep_StringView = 3,
-
-#if UINTPTR_MAX == 0xffffffff
-  kUpb_FieldRep_Pointer = kUpb_FieldRep_4Byte,
-#else
-  kUpb_FieldRep_Pointer = kUpb_FieldRep_8Byte,
-#endif
-
-  kUpb_FieldRep_Shift =
-      6, /* Bit offset of the rep in upb_MiniTable_Field.mode */
+  kUpb_FieldRep_8Byte = 4,
+  kUpb_FieldRep_Shift = 5,  // Bit offset of the rep in upb_MiniTable_Field.mode
 } upb_FieldRep;
 
 UPB_INLINE upb_FieldMode upb_FieldMode_Get(const upb_MiniTable_Field* field) {