83 lines
2.0 KiB
C++
83 lines
2.0 KiB
C++
//===== Copyright c 1996-2008, Valve Corporation, All rights reserved. ======//
|
|
//
|
|
// Purpose: Simple encoder/decoder
|
|
//
|
|
//===========================================================================//
|
|
|
|
#ifndef COMMON_SIMPLE_CODEC
|
|
#define COMMON_SIMPLE_CODEC
|
|
|
|
#include <stdlib.h>
|
|
|
|
namespace SimpleCodec
|
|
{
|
|
|
|
//
|
|
// Encodes the buffer in place
|
|
// pvBuffer pointer to the base of the buffer, buffer length is "numBytes + numSultBytes"
|
|
// numBytes number of real data bytes already in the buffer
|
|
// numSultBytes number of sult bytes to be placed after the buffer data
|
|
//
|
|
inline void EncodeBuffer( unsigned char *pvBuffer, int numBytes, unsigned char numSultBytes )
|
|
{
|
|
unsigned char xx = 0xA7;
|
|
|
|
// Add some sult in the very end
|
|
Assert( numSultBytes > 0 );
|
|
pvBuffer[ numBytes + numSultBytes - 1 ] = numSultBytes;
|
|
-- numSultBytes;
|
|
|
|
// Store sult data
|
|
for ( unsigned char *pvSult = pvBuffer + numBytes;
|
|
numSultBytes -- > 0; ++ pvSult )
|
|
{
|
|
*pvSult = rand() % 0x100;
|
|
xx ^= ( *pvSult + 0xA7 ) % 0x100;
|
|
}
|
|
|
|
// Hash the buffer
|
|
for ( ; numBytes -- > 0; ++ pvBuffer )
|
|
{
|
|
unsigned char v = *pvBuffer;
|
|
v ^= xx;
|
|
xx = ( v + 0xA7 ) % 0x100;
|
|
*pvBuffer = v;
|
|
}
|
|
}
|
|
|
|
//
|
|
// Decodes the buffer in place
|
|
// pvBuffer pointer to the base of the encoded buffer
|
|
// numBytes number of buffer bytes on input
|
|
// on return contains the number of data bytes decoded (excludes sult)
|
|
//
|
|
inline void DecodeBuffer( unsigned char *pvBuffer, int &numBytes )
|
|
{
|
|
unsigned char xx = 0xA7;
|
|
|
|
// Discover the number of sult bytes
|
|
unsigned char numSultBytes = pvBuffer[ numBytes - 1 ];
|
|
numBytes -= numSultBytes;
|
|
-- numSultBytes;
|
|
|
|
// Recover sult data
|
|
for ( unsigned char *pvSult = pvBuffer + numBytes;
|
|
numSultBytes -- > 0; ++ pvSult )
|
|
{
|
|
xx ^= ( *pvSult + 0xA7 ) % 0x100;
|
|
}
|
|
|
|
// Hash the buffer
|
|
for ( int numBufBytes = numBytes; numBufBytes -- > 0; ++ pvBuffer )
|
|
{
|
|
unsigned char v = *pvBuffer;
|
|
v ^= xx;
|
|
xx = ( *pvBuffer + 0xA7 ) % 0x100;
|
|
*pvBuffer = v;
|
|
}
|
|
}
|
|
|
|
|
|
}; // namespace SimpleCodec
|
|
|
|
#endif // COMMON_SIMPLE_CODEC
|