Class LabelMap

paddle/phi/kernels/impl/einsum_kernel_impl.h:76–102

map a label('a' - 'z') -> int64_t, O(1) speed.

// map a label('a' - 'z') -> int64_t, O(1) speed.
class LabelMap {
  constexpr static int N =
      26 + 1;  // 'a' - 'z' + '.', '.' is for broadcast dims
  int64_t default_value;
  int64_t map[N];

 public:
  explicit LabelMap(int64_t default_value = 0) {
    this->default_value = default_value;
    for (size_t i = 0; i < N; ++i) map[i] = default_value;
  }
  int64_t& operator[](int label) {
    int i = label - 'a';
    return map[i];
  }
  int64_t operator[](int label) const {
    int i = label - 'a';
    return map[i];
  }
  bool exist(char label) { return !is_default(label); }

 private:
  // non-exist is present by is_default
  bool is_default(char label) {
    return (*this)[static_cast<int>(label)] == default_value;
  }
};

inline std::string label_to_string(const std::vector<char>& all_labels,
                                   const LabelMap& label2type) {