Efficient dword bitwise rotate / circular shift using Bash shell ?

Example:

rol() { num="$@" ; pre=$((num<<13)) ; suf=$((num>>19)) ;
        num=$((pre^suf)) ; num=$((num&0xffffffff)) ; echo "$num" ; }

What tricks will make this more efficient in Bash?

--
  www.sybershock.com | sci.crypt | alt.sources.crypto | alt.lite.bulb