LC3 Assembly Language TRAPs and Subroutines –Memory Dump

; SHIFTR: A simple assembly language subroutine to shift the value ; in R0 right by one bit. Feel free to use this code as-is ; or modify it for use. ; NOTE - this is not a complete assembly language file, you must ; cut/paste it into your main.asm to use the SHIFTR subroutine. ;================================================================================= ; SHIFTR - Shift the value in R0 right by one bit ;--------------------------------------------------------------------------------- ; R0 is shifted right by one bit ; All other registers (except R7) are callee-saved and restored. ; R7 is modified, as it is with all subroutine calls. ;================================================================================= SHIFTR ST R1, R1SAVE ; Save callee-save registers ST R2, R2SAVE AND R1, R1, #0 ; R1 holds the itermediate result AND R2, R2, #0 ; R2 holds count for number of bits examined ADD R2, R2, #15 NextBit ADD R0, R0, #0 ; Test MSB for 1 or 0 BRn MSBIS1 MSBIS0 ADD R1, R1, R1 ;shift result left ;force LSB to 0 ADD R0, R0, R0 ;shift original value left; check next bit BR TestDone MSBIS1 ADD R1, R1, R1 ;shift running total right ADD R1, R1, #1 ;force LSB to 1 ADD R0, R0, R0 ;shift original value left; check next bit TestDone ADD R2, R2, #-1 BRP NextBit Done ADD R0, R1, #0 ; Move result to R0 LD R2, R2SAVE ; Restore callee-save registers LD R1, R1SAVE RET ; Return to calling program R1SAVE .BLKW 1 R2SAVE .BLKW 1