minetest/src/serialization.cpp

/*
Minetest-c55
Copyright (C) 2010 celeron55, Perttu Ahola <celeron55@gmail.com>

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/

/*
(c) 2010 Perttu Ahola <celeron55@gmail.com>
*/

#include "serialization.h"
#include "utility.h"

void compress(SharedBuffer<u8> data, std::ostream &os, u8 version)
{
	if(data.getSize() == 0)
		return;

	// Write length (u32)

	u8 tmp[4];
	writeU32(tmp, data.getSize());
	os.write((char*)tmp, 4);
	
	// We will be writing 8-bit pairs of more_count and byte
	u8 more_count = 0;
	u8 current_byte = data[0];
	for(u32 i=1; i<data.getSize(); i++)
	{
		if(
			data[i] != current_byte
			|| more_count == 255
		)
		{
			// write count and byte
			os.write((char*)&more_count, 1);
			os.write((char*)&current_byte, 1);
			more_count = 0;
			current_byte = data[i];
		}
		else
		{
			more_count++;
		}
	}
	// write count and byte
	os.write((char*)&more_count, 1);
	os.write((char*)&current_byte, 1);
}

void decompress(std::istream &is, std::ostream &os, u8 version)
{
	// Read length (u32)

	u8 tmp[4];
	is.read((char*)tmp, 4);
	u32 len = readU32(tmp);
	
	// We will be reading 8-bit pairs of more_count and byte
	u32 count = 0;
	for(;;)
	{
		u8 more_count=0;
		u8 byte=0;

		is.read((char*)&more_count, 1);
		
		is.read((char*)&byte, 1);

		if(is.eof())
			throw SerializationError("decompress: stream ended halfway");

		for(s32 i=0; i<(u16)more_count+1; i++)
			os.write((char*)&byte, 1);

		count += (u16)more_count+1;

		if(count == len)
			break;
	}
}