Re: Efficient dword bitwise rotate / circular shift using Bash shell ?

On 2024-05-11 17:37, Phil Carmody wrote:

SugarBug <3883@sugar.bug> writes:

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?

 If you can be sure the input will never be 0xffffffff, then this should
work:
 rol () { echo "$(($1*8192%0xffffffff))" ; }
 Phil
 

rol13() { printf '0x%X' $(((($1<<13)+($1>>19))&0xffffffff))
}
Avoids that limitation, but may be slightly slower depending on bash inefficiencies.
Enjoy
Jakob
--
Jakob Bohm, CIO, Partner, WiseMo A/S.  https://www.wisemo.com
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