How to shift bytes in ARM assembly











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Say I have the following hex values stored in registers;



r1 = #0x1



r2 = #0x2



r3 = #0x3



r4 = #0xA



And I want to store #0x123A in r0.



Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?






assembly arm







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    up vote
    0
    down vote

    favorite












    Say I have the following hex values stored in registers;



    r1 = #0x1



    r2 = #0x2



    r3 = #0x3



    r4 = #0xA



    And I want to store #0x123A in r0.



    Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?






    assembly arm







    share|improve this question
























      up vote
      0
      down vote

      favorite









      up vote
      0
      down vote

      favorite











      Say I have the following hex values stored in registers;



      r1 = #0x1



      r2 = #0x2



      r3 = #0x3



      r4 = #0xA



      And I want to store #0x123A in r0.



      Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?






      assembly arm







      share|improve this question













      Say I have the following hex values stored in registers;



      r1 = #0x1



      r2 = #0x2



      r3 = #0x3



      r4 = #0xA



      And I want to store #0x123A in r0.



      Is there a way of shifting byte values similar to shifting bits with LSL/LSR so that I could AND each register (r1-r4) with a mask and then shift the bytes into correct position in r0?






      assembly arm




      assembly arm






      share|improve this question













      share|improve this question











      share|improve this question




      share|improve this question










      asked Nov 11 at 16:58









      Ciarán

      31




      31
























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          ARM shifts are done as part of the second operand in other operations. So you would do something like:



          OR r0, r4, r3, LSL #4
          
OR r0, r0, r2, LSL #8
          
OR r0, r0, r1, LSL #12


          though this does not do the 'mask' part if the other bits of your source registers are non-zero.






          share|improve this answer





















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            1 Answer
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            active

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            active

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            up vote
            2
            down vote



            accepted










            ARM shifts are done as part of the second operand in other operations. So you would do something like:



            OR r0, r4, r3, LSL #4
            
OR r0, r0, r2, LSL #8
            
OR r0, r0, r1, LSL #12


            though this does not do the 'mask' part if the other bits of your source registers are non-zero.






            share|improve this answer

























              up vote
              2
              down vote



              accepted










              ARM shifts are done as part of the second operand in other operations. So you would do something like:



              OR r0, r4, r3, LSL #4
              
OR r0, r0, r2, LSL #8
              
OR r0, r0, r1, LSL #12


              though this does not do the 'mask' part if the other bits of your source registers are non-zero.






              share|improve this answer























                up vote
                2
                down vote



                accepted







                up vote
                2
                down vote



                accepted






                ARM shifts are done as part of the second operand in other operations. So you would do something like:



                OR r0, r4, r3, LSL #4
                
OR r0, r0, r2, LSL #8
                
OR r0, r0, r1, LSL #12


                though this does not do the 'mask' part if the other bits of your source registers are non-zero.






                share|improve this answer












                ARM shifts are done as part of the second operand in other operations. So you would do something like:



                OR r0, r4, r3, LSL #4
                
OR r0, r0, r2, LSL #8
                
OR r0, r0, r1, LSL #12


                though this does not do the 'mask' part if the other bits of your source registers are non-zero.







                share|improve this answer












                share|improve this answer



                share|improve this answer










                answered Nov 11 at 17:15









                Chris Dodd

                80.1k680159




                80.1k680159






























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