blob: 6108065f1e6ace1164605d66dd32837568a6a0b4 [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 VM_BITFIELD_H_
#define VM_BITFIELD_H_
namespace dart {
static const uword kUwordOne = 1U;
// BitField is a template for encoding and decoding a bit field inside
// an unsigned machine word.
template<typename T, int position, int size>
class BitField {
public:
static const intptr_t kNextBit = position + size;
// Tells whether the provided value fits into the bit field.
static bool is_valid(T value) {
return (static_cast<uword>(value) & ~((kUwordOne << size) - 1)) == 0;
}
// Returns a uword mask of the bit field.
static uword mask() {
return (kUwordOne << size) - 1;
}
// Returns a uword mask of the bit field which can be applied directly to
// to the raw unshifted bits.
static uword 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 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 uword encode(T value) {
ASSERT(is_valid(value));
return static_cast<uword>(value) << position;
}
// Extracts the bit field from the value.
static T decode(uword value) {
return static_cast<T>((value >> position) & ((kUwordOne << 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 uword update(T value, uword original) {
ASSERT(is_valid(value));
return (static_cast<uword>(value) << position) |
(~mask_in_place() & original);
}
};
} // namespace dart
#endif // VM_BITFIELD_H_