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//
// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions
// are met:
// * Redistributions of source code must retain the above copyright
// notice, this list of conditions and the following disclaimer.
// * 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.
// * Neither the name of NVIDIA CORPORATION nor the names of its
// contributors may be used to endorse or promote products derived
// from this software without specific prior written permission.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS ``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 THE COPYRIGHT OWNER 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.
//
// Copyright (c) 2018 NVIDIA Corporation. All rights reserved.
// Copyright (c) 2004-2008 AGEIA Technologies, Inc. All rights reserved.
// Copyright (c) 2001-2004 NovodeX AG. All rights reserved.
#pragma once
#include <PxAssert.h>
#if PX_LINUX_FAMILY
#include <stdint.h> // intptr_t
#endif
template <size_t align>
class StackAllocator
{
typedef unsigned char byte;
// todo: switch to offsets so size is consistent on x64
// mSize is just for book keeping so could be 4 bytes
struct Header
{
Header* mPrev;
size_t mSize : 31;
size_t mFree : 1;
};
StackAllocator(const StackAllocator&);
StackAllocator& operator=(const StackAllocator&);
public:
StackAllocator(void* buffer, size_t bufferSize)
: mBuffer(reinterpret_cast<byte*>(buffer)), mBufferSize(bufferSize), mFreeStart(mBuffer), mTop(0)
{
}
~StackAllocator()
{
PX_ASSERT(userBytes() == 0);
}
void* allocate(size_t numBytes)
{
// this is non-standard
if(!numBytes)
return 0;
uintptr_t unalignedStart = uintptr_t(mFreeStart) + sizeof(Header);
byte* allocStart = reinterpret_cast<byte*>((unalignedStart + (align - 1)) & ~(align - 1));
byte* allocEnd = allocStart + numBytes;
// ensure there is space for the alloc
PX_ASSERT(allocEnd <= mBuffer + mBufferSize);
Header* h = getHeader(allocStart);
h->mPrev = mTop;
h->mSize = numBytes;
h->mFree = false;
mTop = h;
mFreeStart = allocEnd;
return allocStart;
}
void deallocate(void* p)
{
if(!p)
return;
Header* h = getHeader(p);
h->mFree = true;
// unwind the stack to the next live alloc
while(mTop && mTop->mFree)
{
mFreeStart = reinterpret_cast<byte*>(mTop);
mTop = mTop->mPrev;
}
}
private:
// return the header for an allocation
inline Header* getHeader(void* p) const
{
PX_ASSERT((reinterpret_cast<uintptr_t>(p) & (align - 1)) == 0);
PX_ASSERT(reinterpret_cast<byte*>(p) >= mBuffer + sizeof(Header));
PX_ASSERT(reinterpret_cast<byte*>(p) < mBuffer + mBufferSize);
return reinterpret_cast<Header*>(p) - 1;
}
public:
// total user-allocated bytes not including any overhead
size_t userBytes() const
{
size_t total = 0;
Header* iter = mTop;
while(iter)
{
total += iter->mSize;
iter = iter->mPrev;
}
return total;
}
// total user-allocated bytes + overhead
size_t totalUsedBytes() const
{
return mFreeStart - mBuffer;
}
size_t remainingBytes() const
{
return mBufferSize - totalUsedBytes();
}
size_t wastedBytes() const
{
return totalUsedBytes() - userBytes();
}
private:
byte* const mBuffer;
const size_t mBufferSize;
byte* mFreeStart; // start of free space
Header* mTop; // top allocation header
};
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