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93 lines
2.8 KiB
93 lines
2.8 KiB
/*
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* Copyright (C) 2014 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef ART_LIBARTBASE_BASE_BIT_FIELD_H_
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#define ART_LIBARTBASE_BASE_BIT_FIELD_H_
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#include <android-base/logging.h>
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#include "globals.h"
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namespace art {
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static constexpr uintptr_t kUintPtrTOne = 1U;
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// BitField is a template for encoding and decoding a bit field inside
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// an unsigned machine word.
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template<typename T, size_t kPosition, size_t kSize>
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class BitField {
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public:
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typedef T value_type;
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static constexpr size_t position = kPosition;
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static constexpr size_t size = kSize;
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static_assert(position < sizeof(uintptr_t) * kBitsPerByte, "Invalid position.");
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static_assert(size != 0u, "Invalid size.");
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static_assert(size <= sizeof(uintptr_t) * kBitsPerByte, "Invalid size.");
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static_assert(size + position <= sizeof(uintptr_t) * kBitsPerByte, "Invalid position + size.");
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// Tells whether the provided value fits into the bit field.
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static bool IsValid(T value) {
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return (static_cast<uintptr_t>(value) & ~((kUintPtrTOne << size) - 1)) == 0;
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}
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// Returns a uword mask of the bit field.
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static uintptr_t Mask() {
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return (kUintPtrTOne << size) - 1;
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}
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// Returns a uword mask of the bit field which can be applied directly to
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// the raw unshifted bits.
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static uintptr_t MaskInPlace() {
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return ((kUintPtrTOne << size) - 1) << position;
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}
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// Returns the shift count needed to right-shift the bit field to
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// the least-significant bits.
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static int Shift() {
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return position;
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}
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// Returns the size of the bit field.
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static int BitSize() {
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return size;
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}
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// Returns a uword with the bit field value encoded.
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static uintptr_t Encode(T value) {
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DCHECK(IsValid(value));
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return static_cast<uintptr_t>(value) << position;
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}
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// Extracts the bit field from the value.
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static T Decode(uintptr_t value) {
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return static_cast<T>((value >> position) & ((kUintPtrTOne << size) - 1));
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}
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// Returns a uword with the bit field value encoded based on the
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// original value. Only the bits corresponding to this bit field
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// will be changed.
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static uintptr_t Update(T value, uintptr_t original) {
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DCHECK(IsValid(value));
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return (static_cast<uintptr_t>(value) << position) |
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(~MaskInPlace() & original);
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}
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};
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} // namespace art
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#endif // ART_LIBARTBASE_BASE_BIT_FIELD_H_
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