compress.cs

// compress.cs -- compress a memory buffer
// Copyright (C) 1995-2005 Jean-loup Gailly.
// Copyright (C) 2007-2011 by the Authors
// For conditions of distribution and use, see copyright notice in License.txt

using System;

namespace Free.Ports.zLib
{
	public static partial class zlib
	{
		//   The following utility functions are implemented on top of the
		// basic stream-oriented functions. To simplify the interface, some
		// default options are assumed (compression level and memory usage,
		// standard memory allocation functions). The source code of these
		// utility functions can easily be modified if you need special options.

		// ===========================================================================
		// Compresses the source buffer into the destination buffer. The level
		// parameter has the same meaning as in deflateInit.  sourceLen is the byte
		// length of the source buffer. Upon entry, destLen is the total size of the
		// destination buffer, which must be at least 0.1% larger than sourceLen plus
		// 12 bytes. Upon exit, destLen is the actual size of the compressed buffer.
		//
		// compress2 returns Z_OK if success, Z_MEM_ERROR if there was not enough
		// memory, Z_BUF_ERROR if there was not enough room in the output buffer,
		// Z_STREAM_ERROR if the level parameter is invalid.
		
		public static int compress2(byte[] dest, ref uint destLen, byte[] source, uint sourceLen, int level)
		{
			z_stream stream=new z_stream();

			stream.next_in=0;
			stream.in_buf=source;
			stream.avail_in=sourceLen;
			stream.next_out=0;
			stream.out_buf=dest;
			stream.avail_out=destLen;
			if(stream.avail_out!=destLen) return Z_BUF_ERROR;

			int err=deflateInit(stream, level);
			if(err!=Z_OK) return err;

			err=deflate(stream, Z_FINISH);
			if(err!=Z_STREAM_END)
			{
				deflateEnd(stream);
				return err==Z_OK?Z_BUF_ERROR:err;
			}
			destLen=stream.total_out;

			err=deflateEnd(stream);
			return err;
		}

		// ===========================================================================
		//   Compresses the source buffer into the destination buffer.  sourceLen is
		// the byte length of the source buffer. Upon entry, destLen is the total
		// size of the destination buffer, which must be at least the value returned
		// by compressBound(sourceLen). Upon exit, destLen is the actual size of the
		// compressed buffer.

		//   This function can be used to compress a whole file at once if the
		// input file is mmap'ed.
		//   compress returns Z_OK if success, Z_MEM_ERROR if there was not
		// enough memory, Z_BUF_ERROR if there was not enough room in the output
		// buffer.

		public static int compress(byte[] dest, ref uint destLen, byte[] source, uint sourceLen)
		{
			return compress2(dest, ref destLen, source, sourceLen, Z_DEFAULT_COMPRESSION);
		}

		// ===========================================================================
		// If the default memLevel or windowBits for deflateInit() is changed, then
		// this function needs to be updated.
		
		//   compressBound() returns an upper bound on the compressed size after
		// compress() or compress2() on sourceLen bytes.  It would be used before
		// a compress() or compress2() call to allocate the destination buffer.

		public static uint compressBound(uint sourceLen)
		{
			return sourceLen+(sourceLen>>12)+(sourceLen>>14)+(sourceLen>>25)+13;
		}
	}
}