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/*
* Copyright (C) 2010 Apple Inc. All rights reserved.
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* License as published by the Free Software Foundation; either
* version 2 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*
*/
#ifndef Bitmap_h
#define Bitmap_h
#include <array>
#include <wtf/Atomics.h>
#include <wtf/StdLibExtras.h>
#include <stdint.h>
#include <string.h>
namespace WTF {
enum BitmapAtomicMode {
// This makes concurrentTestAndSet behave just like testAndSet.
BitmapNotAtomic,
// This makes concurrentTestAndSet use compareAndSwap, so that it's
// atomic even when used concurrently.
BitmapAtomic
};
template<size_t Size, BitmapAtomicMode atomicMode = BitmapNotAtomic, typename WordType = uint32_t>
class Bitmap {
WTF_MAKE_FAST_ALLOCATED;
public:
Bitmap();
bool get(size_t) const;
void set(size_t);
bool testAndSet(size_t);
bool testAndClear(size_t);
bool concurrentTestAndSet(size_t);
bool concurrentTestAndClear(size_t);
size_t nextPossiblyUnset(size_t) const;
void clear(size_t);
void clearAll();
int64_t findRunOfZeros(size_t) const;
size_t count(size_t = 0) const;
size_t isEmpty() const;
size_t isFull() const;
private:
static const unsigned wordSize = sizeof(WordType) * 8;
static const unsigned words = (Size + wordSize - 1) / wordSize;
// the literal '1' is of type signed int. We want to use an unsigned
// version of the correct size when doing the calculations because if
// WordType is larger than int, '1 << 31' will first be sign extended
// and then casted to unsigned, meaning that set(31) when WordType is
// a 64 bit unsigned int would give 0xffff8000
static const WordType one = 1;
std::array<WordType, words> bits;
};
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline Bitmap<size, atomicMode, WordType>::Bitmap()
{
clearAll();
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline bool Bitmap<size, atomicMode, WordType>::get(size_t n) const
{
return !!(bits[n / wordSize] & (one << (n % wordSize)));
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline void Bitmap<size, atomicMode, WordType>::set(size_t n)
{
bits[n / wordSize] |= (one << (n % wordSize));
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline bool Bitmap<size, atomicMode, WordType>::testAndSet(size_t n)
{
WordType mask = one << (n % wordSize);
size_t index = n / wordSize;
bool result = bits[index] & mask;
bits[index] |= mask;
return result;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline bool Bitmap<size, atomicMode, WordType>::testAndClear(size_t n)
{
WordType mask = one << (n % wordSize);
size_t index = n / wordSize;
bool result = bits[index] & mask;
bits[index] &= ~mask;
return result;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline bool Bitmap<size, atomicMode, WordType>::concurrentTestAndSet(size_t n)
{
if (atomicMode == BitmapNotAtomic)
return testAndSet(n);
ASSERT(atomicMode == BitmapAtomic);
WordType mask = one << (n % wordSize);
size_t index = n / wordSize;
WordType* wordPtr = bits.data() + index;
WordType oldValue;
do {
oldValue = *wordPtr;
if (oldValue & mask)
return true;
} while (!weakCompareAndSwap(wordPtr, oldValue, static_cast<WordType>(oldValue | mask)));
return false;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline bool Bitmap<size, atomicMode, WordType>::concurrentTestAndClear(size_t n)
{
if (atomicMode == BitmapNotAtomic)
return testAndClear(n);
ASSERT(atomicMode == BitmapAtomic);
WordType mask = one << (n % wordSize);
size_t index = n / wordSize;
WordType* wordPtr = bits.data() + index;
WordType oldValue;
do {
oldValue = *wordPtr;
if (!(oldValue & mask))
return false;
} while (!weakCompareAndSwap(wordPtr, oldValue, static_cast<WordType>(oldValue & ~mask)));
return true;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline void Bitmap<size, atomicMode, WordType>::clear(size_t n)
{
bits[n / wordSize] &= ~(one << (n % wordSize));
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline void Bitmap<size, atomicMode, WordType>::clearAll()
{
memset(bits.data(), 0, sizeof(bits));
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline size_t Bitmap<size, atomicMode, WordType>::nextPossiblyUnset(size_t start) const
{
if (!~bits[start / wordSize])
return ((start / wordSize) + 1) * wordSize;
return start + 1;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline int64_t Bitmap<size, atomicMode, WordType>::findRunOfZeros(size_t runLength) const
{
if (!runLength)
runLength = 1;
for (size_t i = 0; i <= (size - runLength) ; i++) {
bool found = true;
for (size_t j = i; j <= (i + runLength - 1) ; j++) {
if (get(j)) {
found = false;
break;
}
}
if (found)
return i;
}
return -1;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline size_t Bitmap<size, atomicMode, WordType>::count(size_t start) const
{
size_t result = 0;
for ( ; (start % wordSize); ++start) {
if (get(start))
++result;
}
for (size_t i = start / wordSize; i < words; ++i)
result += WTF::bitCount(static_cast<unsigned>(bits[i]));
return result;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline size_t Bitmap<size, atomicMode, WordType>::isEmpty() const
{
for (size_t i = 0; i < words; ++i)
if (bits[i])
return false;
return true;
}
template<size_t size, BitmapAtomicMode atomicMode, typename WordType>
inline size_t Bitmap<size, atomicMode, WordType>::isFull() const
{
for (size_t i = 0; i < words; ++i)
if (~bits[i])
return false;
return true;
}
}
#endif
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