bit.h

// Copyright 2022 The Pigweed Authors
//
// 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
//
//     https://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.
 
// Low-level bit operations including std::endian from C++20.
#pragma once
 
#include <climits>
 
#include "lib/stdcompat/bit.h"
 
namespace pw {
 
using ::cpp20::endian;
 
namespace bytes {
 
#define SIZE_OF_IN_BIT(...) (sizeof(__VA_ARGS__) * CHAR_BIT)
 
template <std::size_t kBitWidth, typename T>
constexpr T SignExtend(T nbit_value) {
  static_assert(std::is_integral_v<T>);
  static_assert(kBitWidth < SIZE_OF_IN_BIT(T));
 
  using SignedT = std::make_signed_t<T>;
 
  constexpr std::size_t extension_bits = SIZE_OF_IN_BIT(SignedT) - kBitWidth;
 
  SignedT nbit_temp = static_cast<SignedT>(nbit_value);
  return ((nbit_temp << extension_bits) >> extension_bits);
}
 
template <typename OutType, std::size_t kMsb, std::size_t kLsb, typename InType>
constexpr OutType ExtractBits(InType value) {
  static_assert(kMsb >= kLsb);
  static_assert(kMsb < SIZE_OF_IN_BIT(InType));
 
  constexpr std::size_t kBitWidth = kMsb - kLsb + 1;
  static_assert(kBitWidth <= SIZE_OF_IN_BIT(OutType));
 
  if constexpr (kBitWidth == SIZE_OF_IN_BIT(InType)) {
    return OutType(value);
  } else {
    constexpr OutType mask = OutType((OutType(1) << kBitWidth) - 1);
    return OutType((value >> kLsb) & mask);
  }
}
 
}  // namespace bytes
}  // namespace pw