7. Displaying Binary Bits

• A good way to apply the shift instructions is to display bytes of ASCII strings in binary format.

• For example, if SHL is used,

   

  the highest bit of the operand is copied into the Carry flag each time the byte is shifted to the left.

• The following program displays each of the bits in EAX:

      .DATA                            ; Begin data segment
          Value   DWORD   1234ABCDh    ; sample binary value
          buffer  BYTE    32 dup(0), 0 ; output buffer
  
      .CODE                       ; Begin code segment
          mov eax, Value          ; value to display
          mov ecx,32              ; number of bits in EAX
          mov esi, OFFSET buffer
      next_bit:
          shl eax, 1              ; shift high bit into Carry flag
          mov BYTE PTR [esi], '0' ; display zero by default
          jnc next_byte           ; if no Carry, advance to next byte
          mov BYTE PTR [esi], '1' ; otherwise display 1
      next_byte:
          inc esi                 ; next buffer position
          loop next_bit           ; shift another bit to left
          ; Display output buffer on the screen...
          ; ...