ddnet/src/engine/shared/ringbuffer.cpp

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/* (c) Magnus Auvinen. See licence.txt in the root of the distribution for more information. */
/* If you are missing that file, acquire a complete release at teeworlds.com. */
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#include <base/system.h>
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#include "ringbuffer.h"
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CRingBufferBase::CItem *CRingBufferBase::NextBlock(CItem *pItem)
{
if(pItem->m_pNext)
return pItem->m_pNext;
return m_pFirst;
}
CRingBufferBase::CItem *CRingBufferBase::PrevBlock(CItem *pItem)
{
if(pItem->m_pPrev)
return pItem->m_pPrev;
return m_pLast;
}
CRingBufferBase::CItem *CRingBufferBase::MergeBack(CItem *pItem)
{
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// make sure that this block and previous block is free
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if(!pItem->m_Free || !pItem->m_pPrev || !pItem->m_pPrev->m_Free)
return pItem;
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// merge the blocks
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pItem->m_pPrev->m_Size += pItem->m_Size;
pItem->m_pPrev->m_pNext = pItem->m_pNext;
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// fixup pointers
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if(pItem->m_pNext)
pItem->m_pNext->m_pPrev = pItem->m_pPrev;
else
m_pLast = pItem->m_pPrev;
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if(pItem == m_pProduce)
m_pProduce = pItem->m_pPrev;
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if(pItem == m_pConsume)
m_pConsume = pItem->m_pPrev;
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// return the current block
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return pItem->m_pPrev;
}
void CRingBufferBase::Init(void *pMemory, int Size, int Flags)
{
mem_zero(pMemory, Size);
m_Size = (Size) / sizeof(CItem) * sizeof(CItem);
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m_pFirst = (CItem *)pMemory;
m_pFirst->m_Free = 1;
m_pFirst->m_Size = m_Size;
m_pLast = m_pFirst;
m_pProduce = m_pFirst;
m_pConsume = m_pFirst;
m_Flags = Flags;
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}
void *CRingBufferBase::Allocate(int Size)
{
int WantedSize = (Size + sizeof(CItem) + sizeof(CItem) - 1) / sizeof(CItem) * sizeof(CItem);
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CItem *pBlock = 0;
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// check if we even can fit this block
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if(WantedSize > m_Size)
return 0;
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while(true)
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{
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// check for space
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if(m_pProduce->m_Free)
{
if(m_pProduce->m_Size >= WantedSize)
pBlock = m_pProduce;
else
{
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// wrap around to try to find a block
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if(m_pFirst->m_Free && m_pFirst->m_Size >= WantedSize)
pBlock = m_pFirst;
}
}
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if(pBlock)
break;
else
{
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// we have no block, check our policy and see what todo
if(m_Flags & FLAG_RECYCLE)
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{
if(!PopFirst())
return 0;
}
else
return 0;
}
}
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// okey, we have our block
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// split the block if needed
if(pBlock->m_Size > WantedSize + (int)sizeof(CItem))
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{
CItem *pNewItem = (CItem *)((char *)pBlock + WantedSize);
pNewItem->m_pPrev = pBlock;
pNewItem->m_pNext = pBlock->m_pNext;
if(pNewItem->m_pNext)
pNewItem->m_pNext->m_pPrev = pNewItem;
pBlock->m_pNext = pNewItem;
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pNewItem->m_Free = 1;
pNewItem->m_Size = pBlock->m_Size - WantedSize;
pBlock->m_Size = WantedSize;
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if(!pNewItem->m_pNext)
m_pLast = pNewItem;
}
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// set next block
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m_pProduce = NextBlock(pBlock);
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// set as used and return the item pointer
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pBlock->m_Free = 0;
return (void *)(pBlock + 1);
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}
int CRingBufferBase::PopFirst()
{
if(m_pConsume->m_Free)
return 0;
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// set the free flag
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m_pConsume->m_Free = 1;
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// previous block is also free, merge them
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m_pConsume = MergeBack(m_pConsume);
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// advance the consume pointer
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m_pConsume = NextBlock(m_pConsume);
while(m_pConsume->m_Free && m_pConsume != m_pProduce)
{
m_pConsume = MergeBack(m_pConsume);
m_pConsume = NextBlock(m_pConsume);
}
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// in the case that we have caught up with the produce pointer
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// we might stand on a free block so merge em
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MergeBack(m_pConsume);
return 1;
}
void *CRingBufferBase::Prev(void *pCurrent)
{
CItem *pItem = ((CItem *)pCurrent) - 1;
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while(true)
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{
pItem = PrevBlock(pItem);
if(pItem == m_pProduce)
return 0;
if(!pItem->m_Free)
return pItem + 1;
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}
}
void *CRingBufferBase::Next(void *pCurrent)
{
CItem *pItem = ((CItem *)pCurrent) - 1;
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while(true)
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{
pItem = NextBlock(pItem);
if(pItem == m_pProduce)
return 0;
if(!pItem->m_Free)
return pItem + 1;
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}
}
void *CRingBufferBase::First()
{
if(m_pConsume->m_Free)
return 0;
return (void *)(m_pConsume + 1);
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}
void *CRingBufferBase::Last()
{
return Prev(m_pProduce + 1);
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}