zlib issue | GameDev.net

Hi Folks, Our file format uses zlib to compress/decompress files. Essentially, I'm trying to write a new compress/decompress routine to add my own progress meter. I have two test functions, one that loads a file and compresses it reading via 'fread/fwrite' calls, and another function that compresses by using memcpy. The memory mapping function doesn't return the same size as the other method. I need to get the memory mapping function to work, since this is the situation that is happening in my loading function. Here are the two functions for reference: file:


FILE *fin = fopen (arg.c_str (), "rb");
FILE *fout = fopen (out.c_str (), "wb");

//z_stream
z_stream stream;
memset (&stream, 0, sizeof (stream));

int err = deflateInit (&stream, 6);
if (err != Z_OK)
	printf ("zlib:%s\n", stream.msg);

int input_length = MAGIC_NUMBER;
unsigned char input_buffer [MAGIC_NUMBER];
int output_length = MAGIC_NUMBER;
unsigned char output_buffer [MAGIC_NUMBER];

stream.next_in = input_buffer;
stream.next_out = output_buffer;

stream.avail_in = fread (input_buffer, 1, input_length, fin);
stream.avail_out = MAGIC_NUMBER;

int read = 1, bytescompressed = MAGIC_NUMBER, decompressed = 0;

for (; ;)
{
	if (stream.avail_in == 0)
	{
		stream.avail_in = fread (input_buffer, 1, input_length, fin);
		stream.next_in = input_buffer;

		read ++;
	}

	err = deflate (&stream, Z_NO_FLUSH);

	unsigned long count = output_length - stream.avail_out;
	if (count)
	{
		if (fwrite (output_buffer, 1, count, fout) != count)
		{
			err = Z_ERRNO;
			return err;
		}

		decompressed += count;

		stream.next_out = output_buffer;
		stream.avail_out = output_length;
	}

	if (err != Z_OK)
		break;
}

for (; ;)
{
	err = deflate (&stream, Z_FINISH);
	
	unsigned int count = output_length - stream.avail_out;
	if (count)
	{
		if (fwrite (output_buffer, 1, count, fout) != count)
		{
			err = Z_ERRNO;
			return err;
		}

		decompressed += count;

		stream.next_out = output_buffer;
		stream.avail_out = output_length;
	}

	if (err != Z_OK)
		break;
}

deflateEnd (&stream);
if ((err != Z_OK) && (err != Z_STREAM_END))
{
	printf ("zlib:%i, %s\n", err, stream.msg);
	inflateEnd (&stream);
	return err;
}

printf ("decompressed:%i\n", decompressed);

fclose (fin);
fclose (fout);

memory mapped:


FILE *fin = fopen (arg.c_str (), "rb");
FILE *fout = fopen (out.c_str (), "wb");

int length = filelength (fileno (fin));
int destLength = length*1.001 + 12;

unsigned char *src = new unsigned char [length];
unsigned char *dst = new unsigned char [destLength];

fread (src, 1, length, fin);

//z_stream
z_stream stream;
memset (&stream, 0, sizeof (stream));

int err = deflateInit (&stream, 6);
if (err != Z_OK)
	printf ("zlib:%s\n", stream.msg);

int input_length = MAGIC_NUMBER;
unsigned char input_buffer [MAGIC_NUMBER];
int output_length = MAGIC_NUMBER;
unsigned char output_buffer [MAGIC_NUMBER];

memset (input_buffer, 0, MAGIC_NUMBER);
memset (output_buffer, 0, MAGIC_NUMBER);

stream.next_in = input_buffer;
stream.next_out = output_buffer;

memcpy (input_buffer, src, MAGIC_NUMBER);
stream.avail_in = MAGIC_NUMBER;
stream.avail_out = MAGIC_NUMBER;

int read = 1, bytescompressed = MAGIC_NUMBER, decompressed = 0;

for (; ;)
{
	if (stream.avail_in == 0)
	{
		memset (input_buffer, 0, MAGIC_NUMBER);

		if ((read+1)*MAGIC_NUMBER < length)
		{
			memcpy (input_buffer, src + read*MAGIC_NUMBER, MAGIC_NUMBER);
			stream.avail_in = MAGIC_NUMBER;

			read++;
			bytescompressed += MAGIC_NUMBER;
		}
		else if (bytescompressed == length)
		{
			stream.avail_in = 0;
			stream.next_in = input_buffer;

			read ++;
		}
		else
		{
			int size = length - read*MAGIC_NUMBER;
			memcpy (input_buffer, src + size, MAGIC_NUMBER);
			bytescompressed += size;
			stream.avail_in = size;

			read ++;
		}


		stream.next_in = input_buffer;
	}

	err = deflate (&stream, Z_NO_FLUSH);

	unsigned long count = output_length - stream.avail_out;
	if (count)
	{
		memcpy ((unsigned char*)dst + decompressed, output_buffer, count);
		decompressed += count;

		stream.next_out = output_buffer;
		stream.avail_out = output_length;

		memset (output_buffer, 0, MAGIC_NUMBER);
	}

	if (err != Z_OK)
		break;
}

for (; ;)
{
	err = deflate (&stream, Z_FINISH);
	
	unsigned int count = output_length - stream.avail_out;
	if (count)
	{
		memcpy ((unsigned char*)dst + decompressed, output_buffer, count);
		decompressed += count;

		stream.next_out = output_buffer;
		stream.avail_out = output_length;

		memset (input_buffer, 0, MAGIC_NUMBER);
	}

	if (err != Z_OK)
		break;
}

deflateEnd (&stream);
if ((err != Z_OK) && (err != Z_STREAM_END))
{
	printf ("zlib:%i, %s\n", err, stream.msg);
	inflateEnd (&stream);
	return err;
}

fwrite (dst, 1, decompressed, fout);

fclose (fin);
fclose (fout);

For my test, I used a random pdf file to compress/decompress. Using the file method, the original file is 36393, and compressed its 29750. Working on the file in memory, the compressed version comes out as 28521. The last if functions 'err' returns 1, which means that Z_STREAM_END, but its not producing the same results as the other method? Any ideas, suggestions? Thanks for the help! -brad

Topic Locked