mm-uu-binhex-decode-function is a variable defined in `mm-uu.el'.
Its value is
binhex-decode-region
This variable may be risky if used as a file-local variable.
Documentation:
*Function to binhex decode.
Internal function is done in elisp by default, therefore decoding may
appear to be horribly slow . You can make Gnus use the external Unix
decoder, such as hexbin.
You can customize this variable.