| // Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file |
| // for details. All rights reserved. Use of this source code is governed by a |
| // BSD-style license that can be found in the LICENSE file. |
| |
| #ifndef RUNTIME_VM_BITFIELD_H_ |
| #define RUNTIME_VM_BITFIELD_H_ |
| |
| #include "platform/globals.h" |
| |
| namespace dart { |
| |
| static const uword kUwordOne = 1U; |
| |
| // BitField is a template for encoding and decoding a value of type T |
| // inside a storage of type S. |
| template <typename S, typename T, int position, int size> |
| class BitField { |
| public: |
| static const intptr_t kNextBit = position + size; |
| |
| // Tells whether the provided value fits into the bit field. |
| static bool is_valid(T value) { |
| return (static_cast<S>(value) & ~((kUwordOne << size) - 1)) == 0; |
| } |
| |
| // Returns a S mask of the bit field. |
| static S mask() { return (kUwordOne << size) - 1; } |
| |
| // Returns a S mask of the bit field which can be applied directly to |
| // to the raw unshifted bits. |
| static S mask_in_place() { return ((kUwordOne << 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 an S with the bit field value encoded. |
| static S encode(T value) { |
| COMPILE_ASSERT((sizeof(S) * kBitsPerByte) >= (position + size)); |
| ASSERT(is_valid(value)); |
| return static_cast<S>(value) << position; |
| } |
| |
| // Extracts the bit field from the value. |
| static T decode(S value) { |
| return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); |
| } |
| |
| // Returns an S with the bit field value encoded based on the |
| // original value. Only the bits corresponding to this bit field |
| // will be changed. |
| static S update(T value, S original) { |
| ASSERT(is_valid(value)); |
| return (static_cast<S>(value) << position) | (~mask_in_place() & original); |
| } |
| }; |
| |
| } // namespace dart |
| |
| #endif // RUNTIME_VM_BITFIELD_H_ |