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| - | ====== 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]] | ||
