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/*
* Copyright (C) 2011 Apple Inc. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
* EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
* PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR
* CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
* EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
* PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
* PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
* OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#ifndef PackedIntVector_h
#define PackedIntVector_h
#include <wtf/BitVector.h>
namespace WTF {
// This class allows you to create an array of integers, where those
// integers have only a handful of bits each. It is not meant to be
// efficient in time, but only in space. (Though making it efficient
// in time for power-of-2 values of bitCount would not be difficult.)
// Note that this does not work as expected for signed types, if you
// are relying on the sign being preserved.
template<typename T, unsigned bitCount>
class PackedIntVector {
public:
PackedIntVector()
{
ASSERT(bitCount);
ASSERT(bitCount < sizeof(void*) * 8);
}
PackedIntVector(const PackedIntVector& other)
: m_bits(other.m_bits)
{
}
PackedIntVector& operator=(const PackedIntVector& other)
{
m_bits = other.m_bits;
return *this;
}
size_t size() const
{
return m_bits.size() / bitCount;
}
void ensureSize(size_t numInts)
{
m_bits.ensureSize(numInts * bitCount);
}
void resize(size_t numInts)
{
m_bits.resize(numInts * bitCount);
}
void clearAll()
{
m_bits.clearAll();
}
T get(size_t index) const
{
uintptr_t result = 0;
for (unsigned subIndex = 0; subIndex < bitCount; ++subIndex) {
result <<= 1;
result |= (m_bits.quickGet(index * bitCount + subIndex) ? 1 : 0);
}
return static_cast<T>(result);
}
void set(size_t index, T value)
{
// Do arithmetic using uintptr_t, because (1) we know what it is
// (T might be an enum) and (2) it's the largest integer type that
// is likely to perform decently well.
uintptr_t myValue = static_cast<uintptr_t>(value);
// Preliminary sanity check that the value is not out of range.
ASSERT((myValue & mask()) == myValue);
for (unsigned subIndex = bitCount; subIndex-- > 0;) {
m_bits.quickSet(index * bitCount + subIndex, !!(myValue & 1));
myValue >>= 1;
}
// Final sanity check that we stored what the user thought we
// stored.
ASSERT(get(index) == value);
}
private:
// This returns the mask, and is careful to not step on the wrap-around
// semantics of the shift amount (1 << 32 is 1 since 32 wraps to 0). There
// is the separate question of why you would ever use this to store 32-bit
// or 64-bit values, but it's probably better to have this work as expected
// in such situations regardless.
static uintptr_t mask() { return (static_cast<uintptr_t>(2) << (bitCount - 1)) - 1; }
// Stores integers bit by bit in big endian.
BitVector m_bits;
};
} // namespace WTF
using WTF::PackedIntVector;
#endif // PackedIntVector_h
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