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