These two gems show how to shift bit arrays. The first one is made for the 80386 processor (or above). The second way can run on any processor starting with 8086.
What if you would like to shift a bit array to the right by, for example 3 bits so that 0100100....0101010 becomes 0000100100...0101010. Terje Mathisen suggets the following piece of code which uses SHRD:

;
; Shift a bit array 3 steps to the right
;
; input:
;    cl = shift amount (here 3)
;   ebx = array length
;   esi = array
;
; output:
;   shifted array, esi=last index+4
;
; destorys:
;   eax, edx
;

        mov     cl,3            ; Shift amount
        xor     edx,edx         ; Shift in zero bits at the top
more:
        mov     eax,[esi]
        push    eax             ; Save current dword
        shrd    eax,edx,cl      ; Shift in previous bottom bits
        mov     [esi]
        add     esi,4
        pop     edx             ; Pop back the saved original value
        dec     ebx             ; Check count
        jnz     more

;
; Shift a bit array 1 step left
;
; input:
;   cx = array length
;   bx = offset to array start point
;
; output:
;   shifted array, bx = start point
;
; destroys:
;   nothing
;

        add     bx,cx           ; point to last byte + 1.
        clc                     ; clear carry
more:    
        dec     bx              ; point to next byte
        rcl     [bx],1          ; shift (cf contains extra bit)
        loop    more            ; loop til done...