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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 VM_BITFIELD_H_ | 5 #ifndef VM_BITFIELD_H_ |
6 #define VM_BITFIELD_H_ | 6 #define 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 bit field inside | 12 // BitField is a template for encoding and decoding a bit field inside |
13 // an unsigned machine word. | 13 // an unsigned machine word. |
siva
2016/02/02 19:18:50
Maybe document what 'S' and 'T' are here.
Florian Schneider
2016/02/02 20:46:58
s/an unsigned machine word/an S/
Ivan Posva
2016/02/02 21:14:56
Done.
| |
14 template<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<uword>(value) & ~((kUwordOne << size) - 1)) == 0; | 21 return (static_cast<S>(value) & ~((kUwordOne << size) - 1)) == 0; |
22 } | 22 } |
23 | 23 |
24 // Returns a uword mask of the bit field. | 24 // Returns a S mask of the bit field. |
25 static uword mask() { | 25 static S mask() { |
26 return (kUwordOne << size) - 1; | 26 return (kUwordOne << size) - 1; |
27 } | 27 } |
28 | 28 |
29 // Returns a uword mask of the bit field which can be applied directly to | 29 // Returns a uword mask of the bit field which can be applied directly to |
30 // to the raw unshifted bits. | 30 // to the raw unshifted bits. |
31 static uword mask_in_place() { | 31 static S mask_in_place() { |
32 return ((kUwordOne << size) - 1) << position; | 32 return ((kUwordOne << size) - 1) << position; |
33 } | 33 } |
34 | 34 |
35 // Returns the shift count needed to right-shift the bit field to | 35 // Returns the shift count needed to right-shift the bit field to |
36 // the least-significant bits. | 36 // the least-significant bits. |
37 static int shift() { | 37 static int shift() { |
38 return position; | 38 return position; |
39 } | 39 } |
40 | 40 |
41 // Returns the size of the bit field. | 41 // Returns the size of the bit field. |
42 static int bitsize() { | 42 static int bitsize() { |
43 return size; | 43 return size; |
44 } | 44 } |
45 | 45 |
46 // Returns a uword with the bit field value encoded. | 46 // Returns a S with the bit field value encoded. |
47 static uword encode(T value) { | 47 static S encode(T value) { |
48 ASSERT(is_valid(value)); | 48 ASSERT(is_valid(value)); |
49 return static_cast<uword>(value) << position; | 49 return static_cast<S>(value) << position; |
50 } | 50 } |
51 | 51 |
52 // Extracts the bit field from the value. | 52 // Extracts the bit field from the value. |
53 static T decode(uword value) { | 53 static T decode(S value) { |
54 return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); | 54 return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); |
55 } | 55 } |
56 | 56 |
57 // Returns a uword with the bit field value encoded based on the | 57 // Returns a S with the bit field value encoded based on the |
58 // original value. Only the bits corresponding to this bit field | 58 // original value. Only the bits corresponding to this bit field |
59 // will be changed. | 59 // will be changed. |
60 static uword update(T value, uword original) { | 60 static S update(T value, S original) { |
61 ASSERT(is_valid(value)); | 61 ASSERT(is_valid(value)); |
62 return (static_cast<uword>(value) << position) | | 62 return (static_cast<S>(value) << position) | |
63 (~mask_in_place() & original); | 63 (~mask_in_place() & original); |
64 } | 64 } |
65 }; | 65 }; |
66 | 66 |
67 } // namespace dart | 67 } // namespace dart |
68 | 68 |
69 #endif // VM_BITFIELD_H_ | 69 #endif // VM_BITFIELD_H_ |
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