GNU EXTENSION
       The glibc2 version of this function has the following  additional  fea-
       tures.   If  salt is a character string starting with the three charac-
       ters "$1$" followed by at most eight characters, and optionally  termi-
       nated  by  "$",  then instead of using the DES machine, the glibc crypt
       function uses an MD5-based algorithm,  and  outputs  up  to  34  bytes,
       namely  "$1$<string>$", where "<string>" stands for the up to 8 charac-
       ters following "$1$" in the salt, followed by 22 bytes chosen from  the
       set [a-zA-Z0-9./].  The entire key is significant here (instead of only
       the first 8 bytes).

       Programs using this function must be linked with -lcrypt.