blob: c03337994e52a434f9da60f69b070da04e900e77 [file] [log] [blame]
// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
// for details. All rights reserved. Use of this source code is governed by a
// BSD-style license that can be found in the LICENSE file.
#ifndef RUNTIME_VM_BITFIELD_H_
#define RUNTIME_VM_BITFIELD_H_
#include "platform/assert.h"
#include "platform/globals.h"
namespace dart {
static const uword kUwordOne = 1U;
// BitField is a template for encoding and decoding a value of type T
// inside a storage of type S.
template <typename S, typename T, int position, int size>
class BitField {
public:
typedef T Type;
static_assert((sizeof(S) * kBitsPerByte) >= (position + size),
"BitField does not fit into the type.");
static const intptr_t kNextBit = position + size;
// Tells whether the provided value fits into the bit field.
static constexpr bool is_valid(T value) {
return (static_cast<S>(value) & ~((kUwordOne << size) - 1)) == 0;
}
// Returns a S mask of the bit field.
static constexpr S mask() { return (kUwordOne << size) - 1; }
// Returns a S mask of the bit field which can be applied directly to
// to the raw unshifted bits.
static constexpr S mask_in_place() {
return ((kUwordOne << size) - 1) << position;
}
// Returns the shift count needed to right-shift the bit field to
// the least-significant bits.
static constexpr int shift() { return position; }
// Returns the size of the bit field.
static constexpr int bitsize() { return size; }
// Returns an S with the bit field value encoded.
static UNLESS_DEBUG(constexpr) S encode(T value) {
DEBUG_ASSERT(is_valid(value));
return static_cast<S>(value) << position;
}
// Extracts the bit field from the value.
static constexpr T decode(S value) {
return static_cast<T>((value >> position) & ((kUwordOne << size) - 1));
}
// Returns an S with the bit field value encoded based on the
// original value. Only the bits corresponding to this bit field
// will be changed.
static UNLESS_DEBUG(constexpr) S update(T value, S original) {
DEBUG_ASSERT(is_valid(value));
return (static_cast<S>(value) << position) | (~mask_in_place() & original);
}
};
} // namespace dart
#endif // RUNTIME_VM_BITFIELD_H_