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//
// Copyright 2015 The ANGLE Project Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
//
// BitSetIterator:
// A helper class to quickly bitscan bitsets for set bits.
//
#ifndef COMMON_BITSETITERATOR_H_
#define COMMON_BITSETITERATOR_H_
#include <stdint.h>
#include <bitset>
#include "common/angleutils.h"
#include "common/debug.h"
#include "common/mathutil.h"
#include "common/platform.h"
namespace angle
{
template <size_t N>
class BitSetIterator final
{
public:
BitSetIterator(const std::bitset<N> &bitset);
BitSetIterator(const BitSetIterator &other);
BitSetIterator &operator=(const BitSetIterator &other);
class Iterator final
{
public:
Iterator(const std::bitset<N> &bits);
Iterator &operator++();
bool operator==(const Iterator &other) const;
bool operator!=(const Iterator &other) const;
unsigned long operator*() const { return mCurrentBit; }
private:
unsigned long getNextBit();
static const size_t BitsPerWord = sizeof(unsigned long) * 8;
std::bitset<N> mBits;
unsigned long mCurrentBit;
unsigned long mOffset;
};
Iterator begin() const { return Iterator(mBits); }
Iterator end() const { return Iterator(std::bitset<N>(0)); }
private:
const std::bitset<N> mBits;
};
template <size_t N>
BitSetIterator<N>::BitSetIterator(const std::bitset<N> &bitset)
: mBits(bitset)
{
}
template <size_t N>
BitSetIterator<N>::BitSetIterator(const BitSetIterator &other)
: mBits(other.mBits)
{
}
template <size_t N>
BitSetIterator<N> &BitSetIterator<N>::operator=(const BitSetIterator &other)
{
mBits = other.mBits;
return *this;
}
template <size_t N>
BitSetIterator<N>::Iterator::Iterator(const std::bitset<N> &bits)
: mBits(bits), mCurrentBit(0), mOffset(0)
{
if (bits.any())
{
mCurrentBit = getNextBit();
}
else
{
mOffset = static_cast<unsigned long>(rx::roundUp(N, BitsPerWord));
}
}
template <size_t N>
typename BitSetIterator<N>::Iterator &BitSetIterator<N>::Iterator::operator++()
{
ASSERT(mBits.any());
mBits.set(mCurrentBit - mOffset, 0);
mCurrentBit = getNextBit();
return *this;
}
inline unsigned long ScanForward(unsigned long bits)
{
ASSERT(bits != 0);
#if defined(ANGLE_PLATFORM_WINDOWS)
unsigned long firstBitIndex = 0ul;
unsigned char ret = _BitScanForward(&firstBitIndex, bits);
ASSERT(ret != 0);
return firstBitIndex;
#elif defined(ANGLE_PLATFORM_POSIX)
return static_cast<unsigned long>(__builtin_ctzl(bits));
#else
#error Please implement bit-scan-forward for your platform!
#endif
}
template <size_t N>
bool BitSetIterator<N>::Iterator::operator==(const Iterator &other) const
{
return mOffset == other.mOffset && mBits == other.mBits;
}
template <size_t N>
bool BitSetIterator<N>::Iterator::operator!=(const Iterator &other) const
{
return !(*this == other);
}
template <size_t N>
unsigned long BitSetIterator<N>::Iterator::getNextBit()
{
static std::bitset<N> wordMask(std::numeric_limits<unsigned long>::max());
while (mOffset < N)
{
unsigned long wordBits = (mBits & wordMask).to_ulong();
if (wordBits != 0ul)
{
return ScanForward(wordBits) + mOffset;
}
mBits >>= BitsPerWord;
mOffset += BitsPerWord;
}
return 0;
}
// Helper to avoid needing to specify the template parameter size
template <size_t N>
BitSetIterator<N> IterateBitSet(const std::bitset<N> &bitset)
{
return BitSetIterator<N>(bitset);
}
} // angle
#endif // COMMON_BITSETITERATOR_H_
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