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1 // Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file | 1 // Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file |
2 // for details. All rights reserved. Use of this source code is governed by a | 2 // for details. All rights reserved. Use of this source code is governed by a |
3 // BSD-style license that can be found in the LICENSE file. | 3 // BSD-style license that can be found in the LICENSE file. |
4 | 4 |
5 #ifndef RUNTIME_VM_BITFIELD_H_ | 5 #ifndef RUNTIME_VM_BITFIELD_H_ |
6 #define RUNTIME_VM_BITFIELD_H_ | 6 #define RUNTIME_VM_BITFIELD_H_ |
7 | 7 |
8 namespace dart { | 8 namespace dart { |
9 | 9 |
10 static const uword kUwordOne = 1U; | 10 static const uword kUwordOne = 1U; |
11 | 11 |
12 // BitField is a template for encoding and decoding a value of type T | 12 // BitField is a template for encoding and decoding a value of type T |
13 // inside a storage of type S. | 13 // inside a storage of type S. |
14 template<typename S, typename T, int position, int size> | 14 template <typename S, typename T, int position, int size> |
15 class BitField { | 15 class BitField { |
16 public: | 16 public: |
17 static const intptr_t kNextBit = position + size; | 17 static const intptr_t kNextBit = position + size; |
18 | 18 |
19 // Tells whether the provided value fits into the bit field. | 19 // Tells whether the provided value fits into the bit field. |
20 static bool is_valid(T value) { | 20 static bool is_valid(T value) { |
21 return (static_cast<S>(value) & ~((kUwordOne << size) - 1)) == 0; | 21 return (static_cast<S>(value) & ~((kUwordOne << size) - 1)) == 0; |
22 } | 22 } |
23 | 23 |
24 // Returns a S mask of the bit field. | 24 // Returns a S mask of the bit field. |
25 static S mask() { | 25 static S mask() { return (kUwordOne << size) - 1; } |
26 return (kUwordOne << size) - 1; | |
27 } | |
28 | 26 |
29 // Returns a S mask of the bit field which can be applied directly to | 27 // Returns a S mask of the bit field which can be applied directly to |
30 // to the raw unshifted bits. | 28 // to the raw unshifted bits. |
31 static S mask_in_place() { | 29 static S mask_in_place() { return ((kUwordOne << size) - 1) << position; } |
32 return ((kUwordOne << size) - 1) << position; | |
33 } | |
34 | 30 |
35 // Returns the shift count needed to right-shift the bit field to | 31 // Returns the shift count needed to right-shift the bit field to |
36 // the least-significant bits. | 32 // the least-significant bits. |
37 static int shift() { | 33 static int shift() { return position; } |
38 return position; | |
39 } | |
40 | 34 |
41 // Returns the size of the bit field. | 35 // Returns the size of the bit field. |
42 static int bitsize() { | 36 static int bitsize() { return size; } |
43 return size; | |
44 } | |
45 | 37 |
46 // Returns an S with the bit field value encoded. | 38 // Returns an S with the bit field value encoded. |
47 static S encode(T value) { | 39 static S encode(T value) { |
48 COMPILE_ASSERT((sizeof(S) * kBitsPerByte) >= (position + size)); | 40 COMPILE_ASSERT((sizeof(S) * kBitsPerByte) >= (position + size)); |
49 ASSERT(is_valid(value)); | 41 ASSERT(is_valid(value)); |
50 return static_cast<S>(value) << position; | 42 return static_cast<S>(value) << position; |
51 } | 43 } |
52 | 44 |
53 // Extracts the bit field from the value. | 45 // Extracts the bit field from the value. |
54 static T decode(S value) { | 46 static T decode(S value) { |
55 return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); | 47 return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); |
56 } | 48 } |
57 | 49 |
58 // Returns an S with the bit field value encoded based on the | 50 // Returns an S with the bit field value encoded based on the |
59 // original value. Only the bits corresponding to this bit field | 51 // original value. Only the bits corresponding to this bit field |
60 // will be changed. | 52 // will be changed. |
61 static S update(T value, S original) { | 53 static S update(T value, S original) { |
62 ASSERT(is_valid(value)); | 54 ASSERT(is_valid(value)); |
63 return (static_cast<S>(value) << position) | | 55 return (static_cast<S>(value) << position) | (~mask_in_place() & original); |
64 (~mask_in_place() & original); | |
65 } | 56 } |
66 }; | 57 }; |
67 | 58 |
68 } // namespace dart | 59 } // namespace dart |
69 | 60 |
70 #endif // RUNTIME_VM_BITFIELD_H_ | 61 #endif // RUNTIME_VM_BITFIELD_H_ |
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