File bit_limits.hpp

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// Copyright 2023 Google LLC
//
// 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.

#pragma once

#include <concepts>
#include <cstddef>
#include <limits>

namespace hal {
template<size_t BitWidth, std::integral T>
[[nodiscard]] consteval T generate_field_of_ones()
{
  T result = 0;
  for (size_t i = 0; i < BitWidth; i++) {
    result |= 1 << i;
  }
  return result;
}

template<size_t BitWidth, std::integral int_t>
struct bit_limits
{
  // Check that the bit width is less than or equal to the size of the int_t.
  static_assert(BitWidth <= sizeof(int_t) * 8,
                "The BitWidth exceed the number of bits in the integer type.");

  // Check that bit width is not zero.
  static_assert(BitWidth != 0, "The BitWidth cannot be 0.");

  [[nodiscard]] static constexpr int_t max()
  {
    if constexpr (std::is_signed_v<int_t>) {
      int_t max = generate_field_of_ones<BitWidth, int_t>();
      max = max >> 1;
      return max;
    } else {
      int_t max = generate_field_of_ones<BitWidth, int_t>();
      return max;
    }
  }

  [[nodiscard]] static constexpr int_t min()
  {
    if constexpr (BitWidth == 64) {
      return std::numeric_limits<int_t>::min();
    } else if constexpr (std::is_signed_v<int_t>) {
      int_t min = (1ULL << BitWidth);
      return min;
    } else {
      return 0U;
    }
  }
};
}  // namespace hal