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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
#ifndef ds_BitArray_h
#define ds_BitArray_h
#include "mozilla/MathAlgorithms.h"
#include "mozilla/TemplateLib.h"
#include <limits.h>
#include <string.h>
#include "jstypes.h"
namespace js {
namespace detail {
template <typename WordT>
inline uint_fast8_t CountTrailingZeroes(WordT word);
template <>
inline uint_fast8_t CountTrailingZeroes(uint32_t word) {
return mozilla::CountTrailingZeroes32(word);
}
template <>
inline uint_fast8_t CountTrailingZeroes(uint64_t word) {
return mozilla::CountTrailingZeroes64(word);
}
} // namespace detail
template <size_t nbits>
class BitArray {
public:
// Use a 32 bit word to make it easier to access a BitArray from JIT code.
using WordT = uint32_t;
static const size_t bitsPerElement = sizeof(WordT) * CHAR_BIT;
static const size_t numSlots =
nbits / bitsPerElement + (nbits % bitsPerElement == 0 ? 0 : 1);
private:
static const size_t paddingBits = (numSlots * bitsPerElement) - nbits;
static_assert(paddingBits < bitsPerElement,
"More padding bits than expected.");
static const WordT paddingMask = WordT(-1) >> paddingBits;
WordT map[numSlots];
public:
constexpr BitArray() : map(){};
void clear(bool value) {
memset(map, value ? 0xFF : 0, sizeof(map));
if (value) {
map[numSlots - 1] &= paddingMask;
}
}
inline bool get(size_t offset) const {
size_t index;
WordT mask;
getIndexAndMask(offset, &index, &mask);
MOZ_ASSERT(index < nbits);
return map[index] & mask;
}
void set(size_t offset) {
size_t index;
WordT mask;
getIndexAndMask(offset, &index, &mask);
map[index] |= mask;
}
void unset(size_t offset) {
size_t index;
WordT mask;
getIndexAndMask(offset, &index, &mask);
map[index] &= ~mask;
}
bool isAllClear() const {
for (size_t i = 0; i < numSlots; i++) {
if (map[i]) {
return false;
}
}
return true;
}
// For iterating over the set bits in the bit array, get a word at a time.
WordT getWord(size_t elementIndex) const {
MOZ_ASSERT(elementIndex < nbits);
return map[elementIndex];
}
static void getIndexAndMask(size_t offset, size_t* indexp, WordT* maskp) {
MOZ_ASSERT(offset < nbits);
static_assert(bitsPerElement == 32, "unexpected bitsPerElement value");
*indexp = offset / bitsPerElement;
*maskp = WordT(1) << (offset % bitsPerElement);
}
static size_t offsetOfMap() { return offsetof(BitArray<nbits>, map); }
};
} /* namespace js */
#endif /* ds_BitArray_h */
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