Shift64

    AREA    Shift64, CODE, READONLY
    IMPORT  main
    EXPORT  start

start
    LDR R0, =0x13131313         ; least significant (LS) word
    LDR R1, =0x13131313         ; most significant (MS) word
    LDR R2, =-2                 ; number of places to shift (n)
    LDR R3, =0                  ; number of bits to shift to get bits which move between registers (n most/least significant bits)
    LDR R4, =0                  ; tempValue - the bits which move between registers
    LDR R5, =32                 ;

    CMP R2, #0                  ; if (n<0)
    BLT shiftLeft               ;   go to shiftLeft

shiftRight
    SUB R3, R5, R2              ; 32-n
    MOV R4, R1, LSL R3          ; tempValue
    MOV R0, R0, LSR R2          ; move LS word right by n bits
    ORR R0, R0, R4              ; add tempValue to beginning of LS word
    MOV R1, R1, LSR R2          ; move MS word right by n bits
    B stop

shiftLeft
    SUB R2, R3, R2              ; |n| ; 0-(-n) = n
    SUB R3, R5, R2              ; 32-n
    MOV R4, R0, LSR R3          ; tempValue
    MOV R1, R1, LSL R2          ; move MS word left by n bits
    ORR R1, R1, R4              ; add tempValue to end of MS word
    MOV R0, R0, LSL R2          ; move LS word left by n bits


stop    B   stop


    END