compute CRC of a file at assembly time using directives

Hi guys,
I have this routine in my code to check crc16 of a file:

Code:

    mov cx, SIZE/2-1
    mov bx, 0xffff
  .l1:
    mov ax, [es:si]
    xor bx, ax
    mov dl, 16
  .l2:
    shr bx, 1
    jnc short .l3
    xor bx, 0xa001
  .l3:
    dec dx
    jnz short .l2
    add si, 2
    dec cx
    jnz short .l1

and I have the file itself. I try to add crc, which is calculated automatically during compilation, to its end:

Code:

;. . . executable code and data
;. . .
;. . .
    times SIZE-2-($-$$) db 0
;
; crc computation
;
    crc = 0xffff
    i = 0
    while i < (SIZE/2 - 1)
      load d word from (i)
      crc = crc xor d
      repeat 16
        if crc & 1
          crc = (crc shr 1) xor 0xa001
        else
          crc = crc shr 1
        end if
      end repeat
      i = i + 2
    end while
    dw crc

But second piece of code doesn't work. It generates result as if "if crc & 1" always true, and "else" part is never executed. Why is it so? I already tried changing & to "and", tried "if (crc - (crc-1) = 0"... even tried WHILE directive instead of IF... but the result is always incorrect.
What am I doing wrong? Please, help