text: /*
   * Copyright (C) 2014 The Android Open Source Project
   *
   * 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 ART_RUNTIME_BASE_BIT_FIELD_H_
  #define ART_RUNTIME_BASE_BIT_FIELD_H_
  
  #include "globals.h"
  #include "logging.h"
  
  namespace art {
  
  static constexpr uintptr_t kUintPtrTOne = 1U;
  
  // BitField is a template for encoding and decoding a bit field inside
  // an unsigned machine word.
  template<typename T, size_t kPosition, size_t kSize>
  class BitField {
   public:
    typedef T value_type;
    static constexpr size_t position = kPosition;
    static constexpr size_t size = kSize;
  
    static_assert(position < sizeof(uintptr_t) * kBitsPerByte, "Invalid position.");
    static_assert(size != 0u, "Invalid size.");
    static_assert(size <= sizeof(uintptr_t) * kBitsPerByte, "Invalid size.");
    static_assert(size + position <= sizeof(uintptr_t) * kBitsPerByte, "Invalid position + size.");
  
    // Tells whether the provided value fits into the bit field.
    static bool IsValid(T value) {
      return (static_cast<uintptr_t>(value) & ~((kUintPtrTOne << size) - 1)) == 0;
    }
  
    // Returns a uword mask of the bit field.
    static uintptr_t Mask() {
      return (kUintPtrTOne << size) - 1;
    }
  
    // Returns a uword mask of the bit field which can be applied directly to
    // the raw unshifted bits.
    static uintptr_t MaskInPlace() {
      return ((kUintPtrTOne << size) - 1) << position;
    }
  
    // Returns the shift count needed to right-shift the bit field to
    // the least-significant bits.
    static int Shift() {
      return position;
    }
  
    // Returns the size of the bit field.
    static int BitSize() {
      return size;
    }
  
    // Returns a uword with the bit field value encoded.
    static uintptr_t Encode(T value) {
      DCHECK(IsValid(value));
      return static_cast<uintptr_t>(value) << position;
    }
  
    // Extracts the bit field from the value.
    static T Decode(uintptr_t value) {
      return static_cast<T>((value >> position) & ((kUintPtrTOne << size) - 1));
    }
  
    // Returns a uword with the bit field value encoded based on the
    // original value. Only the bits corresponding to this bit field
    // will be changed.
    static uintptr_t Update(T value, uintptr_t original) {
      DCHECK(IsValid(value));
      return (static_cast<uintptr_t>(value) << position) |
          (~MaskInPlace() & original);
    }
  };
  
  }  // namespace art
  
  #endif  // ART_RUNTIME_BASE_BIT_FIELD_H_
  