====== Packed BCD Addition ======

The following addition function assumes that both BCD numbers are stored with their least significant digits at the lowest address, and both numbers must have the same length.

<code z80>
;Input:  HL = base address of addend, DE = base address of adder, B = length of numbers
;Output: Addend replaced by addend plus adder

        ld      A, B
        or      A
        ret     z	;test whether length = 0
Loop:   ld      A, (DE)	;get byte of adder
        adc     A, (HL)	;add it to addend, care for carry
        daa		;convert to BCD-decimal
        ld      (HL), A	;save number back in addend
        inc     HL	;next number
        inc     DE
        djnz    Loop   	;continue until all bytes summed
        ret
</code>

**Source**: Icarus Productions' [[http://icarus.ticalc.org/articles/z80_faq.html|Z80 FAQ]]