ruy/side_pair.h

/* Copyright 2019 Google LLC. All Rights Reserved.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/

#ifndef RUY_RUY_SIDE_PAIR_H_
#define RUY_RUY_SIDE_PAIR_H_

#include "ruy/check_macros.h"

namespace ruy {

// Enumeration of the sides, i.e. the operands 'slots', in a matrix
// multiplication. The numerical values of these enumeration constants matter
// because these will be used as indices into the array underlying a SidePair.
enum class Side {
  // Left-hand side
  kLhs = 0,
  // Right-hand side
  kRhs = 1
};

inline Side OtherSide(Side side) {
  return side == Side::kLhs ? Side::kRhs : Side::kLhs;
}

// SidePair is a pair container where the two elements are indexed by a Side
// enum.
template <typename T>
class SidePair final {
 public:
  SidePair() {}
  SidePair(const T& a, const T& b) : elem_{a, b} {}
  const T& operator[](Side side) const {
    const int index = static_cast<int>(side);
    // Technically this check is vacuous, since other values would be
    // out-of-range for enum Side.
    RUY_DCHECK(index == 0 || index == 1);
    return elem_[index];
  }

  T& operator[](Side side) {
    const int index = static_cast<int>(side);
    // Technically this check is vacuous, since other values would be
    // out-of-range for enum Side.
    RUY_DCHECK(index == 0 || index == 1);
    return elem_[index];
  }

 private:
  static_assert(static_cast<int>(Side::kLhs) == 0, "");
  static_assert(static_cast<int>(Side::kRhs) == 1, "");
  T elem_[2];
};

}  // namespace ruy

#endif  // RUY_RUY_SIDE_PAIR_H_