Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2014 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | #ifndef ART_RUNTIME_BASE_BIT_FIELD_H_ |
| 18 | #define ART_RUNTIME_BASE_BIT_FIELD_H_ |
| 19 | |
| 20 | #include "globals.h" |
| 21 | #include "logging.h" |
| 22 | |
| 23 | namespace art { |
| 24 | |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 25 | static constexpr uintptr_t kUintPtrTOne = 1U; |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 26 | |
| 27 | // BitField is a template for encoding and decoding a bit field inside |
| 28 | // an unsigned machine word. |
| 29 | template<typename T, int position, int size> |
| 30 | class BitField { |
| 31 | public: |
| 32 | // Tells whether the provided value fits into the bit field. |
| 33 | static bool IsValid(T value) { |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 34 | return (static_cast<uintptr_t>(value) & ~((kUintPtrTOne << size) - 1)) == 0; |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 35 | } |
| 36 | |
| 37 | // Returns a uword mask of the bit field. |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 38 | static uintptr_t Mask() { |
| 39 | return (kUintPtrTOne << size) - 1; |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 40 | } |
| 41 | |
| 42 | // Returns a uword mask of the bit field which can be applied directly to |
| 43 | // the raw unshifted bits. |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 44 | static uintptr_t MaskInPlace() { |
| 45 | return ((kUintPtrTOne << size) - 1) << position; |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 46 | } |
| 47 | |
| 48 | // Returns the shift count needed to right-shift the bit field to |
| 49 | // the least-significant bits. |
| 50 | static int Shift() { |
| 51 | return position; |
| 52 | } |
| 53 | |
| 54 | // Returns the size of the bit field. |
| 55 | static int BitSize() { |
| 56 | return size; |
| 57 | } |
| 58 | |
| 59 | // Returns a uword with the bit field value encoded. |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 60 | static uintptr_t Encode(T value) { |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 61 | DCHECK(IsValid(value)); |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 62 | return static_cast<uintptr_t>(value) << position; |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 63 | } |
| 64 | |
| 65 | // Extracts the bit field from the value. |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 66 | static T Decode(uintptr_t value) { |
| 67 | return static_cast<T>((value >> position) & ((kUintPtrTOne << size) - 1)); |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 68 | } |
| 69 | |
| 70 | // Returns a uword with the bit field value encoded based on the |
| 71 | // original value. Only the bits corresponding to this bit field |
| 72 | // will be changed. |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 73 | static uintptr_t Update(T value, uintptr_t original) { |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 74 | DCHECK(IsValid(value)); |
Ian Rogers | 1373595 | 2014-10-08 12:43:28 -0700 | [diff] [blame] | 75 | return (static_cast<uintptr_t>(value) << position) | |
Nicolas Geoffray | 01bc96d | 2014-04-11 17:43:50 +0100 | [diff] [blame] | 76 | (~MaskInPlace() & original); |
| 77 | } |
| 78 | }; |
| 79 | |
| 80 | } // namespace art |
| 81 | |
| 82 | #endif // ART_RUNTIME_BASE_BIT_FIELD_H_ |