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  • Efficient dword bitwise rotate / circular shift using Bash shell ?

    From SugarBug@21:1/5 to All on Sat May 4 09:24:12 2024
    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?

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  • From Phil Carmody@21:1/5 to SugarBug on Sat May 11 18:37:40 2024
    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
    --
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  • From Jakob Bohm@21:1/5 to Phil Carmody on Wed May 15 13:33:01 2024
    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
    Transformervej 29, 2860 Søborg, Denmark. Direct +45 31 13 16 10
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