ddnet/src/engine/shared/huffman.cpp

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2010-05-29 07:25:38 +00:00
#include <base/system.h>
#include "huffman.h"
struct CHuffmanConstructNode
{
unsigned short m_NodeId;
int m_Frequency;
};
void CHuffman::Setbits_r(CNode *pNode, int Bits, int Depth)
{
if(pNode->m_aLeafs[1] != 0xffff)
Setbits_r(&m_aNodes[pNode->m_aLeafs[1]], Bits|(1<<Depth), Depth+1);
if(pNode->m_aLeafs[0] != 0xffff)
Setbits_r(&m_aNodes[pNode->m_aLeafs[0]], Bits, Depth+1);
if(pNode->m_NumBits)
{
pNode->m_Bits = Bits;
pNode->m_NumBits = Depth;
}
}
// TODO: this should be something faster, but it's enough for now
static void BubbleSort(CHuffmanConstructNode **ppList, int Size)
{
int Changed = 1;
CHuffmanConstructNode *pTemp;
while(Changed)
{
Changed = 0;
for(int i = 0; i < Size-1; i++)
{
if(ppList[i]->m_Frequency < ppList[i+1]->m_Frequency)
{
pTemp = ppList[i];
ppList[i] = ppList[i+1];
ppList[i+1] = pTemp;
Changed = 1;
}
}
}
}
void CHuffman::ConstructTree(const unsigned *pFrequencies)
{
CHuffmanConstructNode aNodesLeftStorage[HUFFMAN_MAX_SYMBOLS];
CHuffmanConstructNode *apNodesLeft[HUFFMAN_MAX_SYMBOLS];
int NumNodesLeft = HUFFMAN_MAX_SYMBOLS;
// add the symbols
for(int i = 0; i < HUFFMAN_MAX_SYMBOLS; i++)
{
m_aNodes[i].m_NumBits = -1;
m_aNodes[i].m_Symbol = i;
m_aNodes[i].m_aLeafs[0] = -1;
m_aNodes[i].m_aLeafs[1] = -1;
if(i == HUFFMAN_EOF_SYMBOL)
aNodesLeftStorage[i].m_Frequency = 1;
else
aNodesLeftStorage[i].m_Frequency = pFrequencies[i];
aNodesLeftStorage[i].m_NodeId = i;
apNodesLeft[i] = &aNodesLeftStorage[i];
}
m_NumNodes = HUFFMAN_MAX_SYMBOLS;
// construct the table
while(NumNodesLeft > 1)
{
// we can't rely on stdlib's qsort for this, it can generate different results on different implementations
BubbleSort(apNodesLeft, NumNodesLeft);
m_aNodes[m_NumNodes].m_NumBits = 0;
m_aNodes[m_NumNodes].m_aLeafs[0] = apNodesLeft[NumNodesLeft-1]->m_NodeId;
m_aNodes[m_NumNodes].m_aLeafs[1] = apNodesLeft[NumNodesLeft-2]->m_NodeId;
apNodesLeft[NumNodesLeft-2]->m_NodeId = m_NumNodes;
apNodesLeft[NumNodesLeft-2]->m_Frequency = apNodesLeft[NumNodesLeft-1]->m_Frequency + apNodesLeft[NumNodesLeft-2]->m_Frequency;
m_NumNodes++;
NumNodesLeft--;
}
// set start node
m_pStartNode = &m_aNodes[m_NumNodes-1];
// build symbol bits
Setbits_r(m_pStartNode, 0, 0);
}
void CHuffman::Init(const unsigned *pFrequencies)
{
int i;
// make sure to cleanout every thing
mem_zero(this, sizeof(*this));
// construct the tree
ConstructTree(pFrequencies);
// build decode LUT
for(i = 0; i < HUFFMAN_LUTSIZE; i++)
{
unsigned Bits = i;
int k;
CNode *pNode = m_pStartNode;
for(k = 0; k < HUFFMAN_LUTBITS; k++)
{
pNode = &m_aNodes[pNode->m_aLeafs[Bits&1]];
Bits >>= 1;
if(!pNode)
break;
if(pNode->m_NumBits)
{
m_apDecodeLut[i] = pNode;
break;
}
}
if(k == HUFFMAN_LUTBITS)
m_apDecodeLut[i] = pNode;
}
}
//***************************************************************
int CHuffman::Compress(const void *pInput, int InputSize, void *pOutput, int OutputSize)
{
// this macro loads a symbol for a byte into bits and bitcount
#define HUFFMAN_MACRO_LOADSYMBOL(Sym) \
Bits |= m_aNodes[Sym].m_Bits << Bitcount; \
Bitcount += m_aNodes[Sym].m_NumBits;
// this macro writes the symbol stored in bits and bitcount to the dst pointer
#define HUFFMAN_MACRO_WRITE() \
while(Bitcount >= 8) \
{ \
*pDst++ = (unsigned char)(Bits&0xff); \
if(pDst == pDstEnd) \
return -1; \
Bits >>= 8; \
Bitcount -= 8; \
}
// setup buffer pointers
const unsigned char *pSrc = (const unsigned char *)pInput;
const unsigned char *pSrcEnd = pSrc + InputSize;
unsigned char *pDst = (unsigned char *)pOutput;
unsigned char *pDstEnd = pDst + OutputSize;
// symbol variables
unsigned Bits = 0;
unsigned Bitcount = 0;
// make sure that we have data that we want to compress
if(InputSize)
{
// {A} load the first symbol
int Symbol = *pSrc++;
while(pSrc != pSrcEnd)
{
// {B} load the symbol
HUFFMAN_MACRO_LOADSYMBOL(Symbol)
// {C} fetch next symbol, this is done here because it will reduce dependency in the code
Symbol = *pSrc++;
// {B} write the symbol loaded at
HUFFMAN_MACRO_WRITE()
}
// write the last symbol loaded from {C} or {A} in the case of only 1 byte input buffer
HUFFMAN_MACRO_LOADSYMBOL(Symbol)
HUFFMAN_MACRO_WRITE()
}
// write EOF symbol
HUFFMAN_MACRO_LOADSYMBOL(HUFFMAN_EOF_SYMBOL)
HUFFMAN_MACRO_WRITE()
// write out the last bits
*pDst++ = Bits;
// return the size of the output
return (int)(pDst - (const unsigned char *)pOutput);
// remove macros
#undef HUFFMAN_MACRO_LOADSYMBOL
#undef HUFFMAN_MACRO_WRITE
}
//***************************************************************
int CHuffman::Decompress(const void *pInput, int InputSize, void *pOutput, int OutputSize)
{
// setup buffer pointers
unsigned char *pDst = (unsigned char *)pOutput;
unsigned char *pSrc = (unsigned char *)pInput;
unsigned char *pDstEnd = pDst + OutputSize;
unsigned char *pSrcEnd = pSrc + InputSize;
unsigned Bits = 0;
unsigned Bitcount = 0;
CNode *pEof = &m_aNodes[HUFFMAN_EOF_SYMBOL];
CNode *pNode = 0;
while(1)
{
// {A} try to load a node now, this will reduce dependency at location {D}
pNode = 0;
if(Bitcount >= HUFFMAN_LUTBITS)
pNode = m_apDecodeLut[Bits&HUFFMAN_LUTMASK];
// {B} fill with new bits
while(Bitcount < 24 && pSrc != pSrcEnd)
{
Bits |= (*pSrc++) << Bitcount;
Bitcount += 8;
}
// {C} load symbol now if we didn't that earlier at location {A}
if(!pNode)
pNode = m_apDecodeLut[Bits&HUFFMAN_LUTMASK];
// {D} check if we hit a symbol already
if(pNode->m_NumBits)
{
// remove the bits for that symbol
Bits >>= pNode->m_NumBits;
Bitcount -= pNode->m_NumBits;
}
else
{
// remove the bits that the lut checked up for us
Bits >>= HUFFMAN_LUTBITS;
Bitcount -= HUFFMAN_LUTBITS;
// walk the tree bit by bit
while(1)
{
// traverse tree
pNode = &m_aNodes[pNode->m_aLeafs[Bits&1]];
// remove bit
Bitcount--;
Bits >>= 1;
// check if we hit a symbol
if(pNode->m_NumBits)
break;
// no more bits, decoding error
if(Bitcount == 0)
return -1;
}
}
// check for eof
if(pNode == pEof)
break;
// output character
if(pDst == pDstEnd)
return -1;
*pDst++ = pNode->m_Symbol;
}
// return the size of the decompressed buffer
return (int)(pDst - (const unsigned char *)pOutput);
}