ddnet/src/engine/shared/compression.cpp

106 lines
2.4 KiB
C++

/* (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. */
#include <base/system.h>
#include "compression.h"
#include <iterator> // std::size
// Format: ESDDDDDD EDDDDDDD EDD... Extended, Data, Sign
unsigned char *CVariableInt::Pack(unsigned char *pDst, int i, int DstSize)
{
if(DstSize <= 0)
return 0;
DstSize--;
*pDst = 0;
if(i < 0)
{
*pDst |= 0x40; // set sign bit
i = ~i;
}
*pDst |= i & 0x3F; // pack 6bit into dst
i >>= 6; // discard 6 bits
while(i)
{
if(DstSize <= 0)
return 0;
*pDst |= 0x80; // set extend bit
DstSize--;
pDst++;
*pDst = i & 0x7F; // pack 7bit
i >>= 7; // discard 7 bits
}
pDst++;
return pDst;
}
const unsigned char *CVariableInt::Unpack(const unsigned char *pSrc, int *pInOut, int SrcSize)
{
if(SrcSize <= 0)
return 0;
const int Sign = (*pSrc >> 6) & 1;
*pInOut = *pSrc & 0x3F;
SrcSize--;
static const int s_aMasks[] = {0x7F, 0x7F, 0x7F, 0x0F};
static const int s_aShifts[] = {6, 6 + 7, 6 + 7 + 7, 6 + 7 + 7 + 7};
for(unsigned i = 0; i < std::size(s_aMasks); i++)
{
if(!(*pSrc & 0x80))
break;
if(SrcSize <= 0)
return 0;
SrcSize--;
pSrc++;
*pInOut |= (*pSrc & s_aMasks[i]) << s_aShifts[i];
}
pSrc++;
*pInOut ^= -Sign; // if(sign) *i = ~(*i)
return pSrc;
}
long CVariableInt::Decompress(const void *pSrc_, int SrcSize, void *pDst_, int DstSize)
{
dbg_assert(DstSize % sizeof(int) == 0, "invalid bounds");
const unsigned char *pSrc = (unsigned char *)pSrc_;
const unsigned char *pSrcEnd = pSrc + SrcSize;
int *pDst = (int *)pDst_;
const int *pDstEnd = pDst + DstSize / sizeof(int);
while(pSrc < pSrcEnd)
{
if(pDst >= pDstEnd)
return -1;
pSrc = CVariableInt::Unpack(pSrc, pDst, pSrcEnd - pSrc);
if(!pSrc)
return -1;
pDst++;
}
return (long)((unsigned char *)pDst - (unsigned char *)pDst_);
}
long CVariableInt::Compress(const void *pSrc_, int SrcSize, void *pDst_, int DstSize)
{
dbg_assert(SrcSize % sizeof(int) == 0, "invalid bounds");
const int *pSrc = (int *)pSrc_;
unsigned char *pDst = (unsigned char *)pDst_;
const unsigned char *pDstEnd = pDst + DstSize;
SrcSize /= sizeof(int);
while(SrcSize)
{
pDst = CVariableInt::Pack(pDst, *pSrc, pDstEnd - pDst);
if(!pDst)
return -1;
SrcSize--;
pSrc++;
}
return (long)(pDst - (unsigned char *)pDst_);
}