This fwex tool extracts the payloads from Broadcom firmware update files.

The first payload image is usually the ROMD CFE/Kernel/root file-system combination.
If the payload is LZW (typically the second payload image is the XML router configuration) it will also decompress it.

The LZW (de)compressor code originally came from the FFMPEG project and was modified by Broadcom for
(de)compressing device configuration files.

In the Zyxel/MitraStar/Broadcom source-code packages provided by those companies there is a tool
that runs on the host for LZW compression only:

hostTools/CompressConfig

That tool includes the FFMPEG library code but does NOT provide its own source-code, as it should
since the files are licensed on the terms of the GNU GPL.

I've copied the files from the Zyxel source-code distribution as the basis of this host-based extractor tool:

 cp userspace/public/libs/cms_util/lzw*.c .
 cp userspace/public/include/cms_lzw.h .
 cp userspace/public/include/linux/os_defs.h .
 cp userspace/public/include/cms{params,version}.h .
 cp userspace/public/include/cms.h .
 cp shared/opensource/include/bcm963xx/bcmTag.h .