PxBitUtils.h

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// Copyright (c) 2004-2008 AGEIA Technologies, Inc. All rights reserved.
// Copyright (c) 2001-2004 NovodeX AG. All rights reserved.

#ifndef PX_BIT_UTILS_H
#define PX_BIT_UTILS_H

#include "foundation/PxMathIntrinsics.h"
#include "foundation/PxAssert.h"
#include "foundation/PxIntrinsics.h"
#include "foundation/PxMathIntrinsics.h"

#if !PX_DOXYGEN
namespace physx
{
#endif
PX_INLINE uint32_t PxBitCount(uint32_t v)
{
    // from http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
    uint32_t const w = v - ((v >> 1) & 0x55555555);
    uint32_t const x = (w & 0x33333333) + ((w >> 2) & 0x33333333);
    return (((x + (x >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
}

PX_INLINE bool PxIsPowerOfTwo(uint32_t x)
{
    return x != 0 && (x & (x - 1)) == 0;
}

// "Next Largest Power of 2
// Given a binary integer value x, the next largest power of 2 can be computed by a SWAR algorithm
// that recursively "folds" the upper bits into the lower bits. This process yields a bit vector with
// the same most significant 1 as x, but all 1's below it. Adding 1 to that value yields the next
// largest power of 2. For a 32-bit value:"
PX_INLINE uint32_t PxNextPowerOfTwo(uint32_t x)
{
    x |= (x >> 1);
    x |= (x >> 2);
    x |= (x >> 4);
    x |= (x >> 8);
    x |= (x >> 16);
    return x + 1;
}

PX_INLINE uint32_t PxLowestSetBit(uint32_t x)
{
    PX_ASSERT(x);
    return PxLowestSetBitUnsafe(x);
}

PX_INLINE uint32_t PxHighestSetBit(uint32_t x)
{
    PX_ASSERT(x);
    return PxHighestSetBitUnsafe(x);
}

// Helper function to approximate log2 of an integer value
// assumes that the input is actually power of two.
PX_INLINE uint32_t PxILog2(uint32_t num)
{
    for(uint32_t i = 0; i < 32; i++)
    {
        num >>= 1;
        if(num == 0)
            return i;
    }

    PX_ASSERT(0);
    return uint32_t(-1);
}

#if !PX_DOXYGEN
} // namespace physx
#endif

#endif