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Diffstat (limited to 'runtime/base/bit_field.h')
-rw-r--r-- | runtime/base/bit_field.h | 82 |
1 files changed, 82 insertions, 0 deletions
diff --git a/runtime/base/bit_field.h b/runtime/base/bit_field.h new file mode 100644 index 0000000..e041bd0 --- /dev/null +++ b/runtime/base/bit_field.h @@ -0,0 +1,82 @@ +/* + * 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_RUNTIME_BASE_BIT_FIELD_H_ +#define ART_RUNTIME_BASE_BIT_FIELD_H_ + +#include "globals.h" +#include "logging.h" + +namespace art { + +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: + // Tells whether the provided value fits into the bit field. + static bool IsValid(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 + // the raw unshifted bits. + static uword MaskInPlace() { + 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) { + DCHECK(IsValid(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) { + DCHECK(IsValid(value)); + return (static_cast<uword>(value) << position) | + (~MaskInPlace() & original); + } +}; + +} // namespace art + +#endif // ART_RUNTIME_BASE_BIT_FIELD_H_ |