====== Packed BCD Subtraction ======

The following code subtracts one number (ARG1) from another (ARG2), both of which are packed BCD format and of equal (but varying) length. The result is stored in the location of the minuend (HL):

<code z80>
BCDPAK:    LD   B,COUNT   ;LENGTH OF TWO ARGUMENTS
           LD   HL,ARG1   ;ADDRESS OF MINUEND
           LD   DE,ARG2   ;ADDRESS OF SUBTRAHEND      
           AND  A         ;CLEAR CARRY
MINUS:     LD   A,(DE)    ;SUBTRAHEND TO ACCUMULATOR 
           SBC  A (HL)    ;SUBTRACT (HL) FROM ACCUMULATOR
           DAA            ;ADJUST RESULT TO DECIMAL CODED VALUE
           LD   (HL),A    ;STORE RESULT
           INC  DE        ;ADVANCE MEMORY POINTERS
           INC  HL
           DJNZ MINUS     ;DEC B, LOOP UNTIL B = 0
</code>

**Source:** Adapted from Zaks' //Programming the Z80//