  void xcheck(uint32_t internal, uint32_t external) {
    EXPECT_EQ(HeaderTable::toExternal(head_, length_, internal), external);
    EXPECT_EQ(HeaderTable::toInternal(head_, length_, external), internal);
  }
  void xcheck(uint32_t internal, uint32_t external) {
    EXPECT_EQ(HeaderTable::toExternal(head_, length_, internal), external);
    EXPECT_EQ(HeaderTable::toInternal(head_, length_, external), internal);
  }