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 25 static const uword kUwordOne = 1U; 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. IsValid(T value)33 static bool IsValid(T value) { 34 return (static_cast<uword>(value) & ~((kUwordOne << size) - 1)) == 0; 35 } 36 37 // Returns a uword mask of the bit field. Mask()38 static uword Mask() { 39 return (kUwordOne << size) - 1; 40 } 41 42 // Returns a uword mask of the bit field which can be applied directly to 43 // the raw unshifted bits. MaskInPlace()44 static uword MaskInPlace() { 45 return ((kUwordOne << size) - 1) << position; 46 } 47 48 // Returns the shift count needed to right-shift the bit field to 49 // the least-significant bits. Shift()50 static int Shift() { 51 return position; 52 } 53 54 // Returns the size of the bit field. BitSize()55 static int BitSize() { 56 return size; 57 } 58 59 // Returns a uword with the bit field value encoded. Encode(T value)60 static uword Encode(T value) { 61 DCHECK(IsValid(value)); 62 return static_cast<uword>(value) << position; 63 } 64 65 // Extracts the bit field from the value. Decode(uword value)66 static T Decode(uword value) { 67 return static_cast<T>((value >> position) & ((kUwordOne << size) - 1)); 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. Update(T value,uword original)73 static uword Update(T value, uword original) { 74 DCHECK(IsValid(value)); 75 return (static_cast<uword>(value) << position) | 76 (~MaskInPlace() & original); 77 } 78 }; 79 80 } // namespace art 81 82 #endif // ART_RUNTIME_BASE_BIT_FIELD_H_ 83