Talk:Converting Binary Coded Decimal
More efficient variants?
The given routines (counting up/down by 1) seem a whole waste of cpu cycles to me ...
My would suggest as replacement (or at least as additional variants):
(Alas, these variants needs an extra memory location.)
\ Convert binary number to BCD \ ---------------------------- \ On entry, A=value 0-99 \ On exit, A=BCD value &00-&99 \ X, Y, tmp corrupted .BINtoBCD SED :\ decimal mode LDY #0 :\ init. bcd value ASL:ORA #1 :\ end marker .loop TAX :\ save binary value TYA :\ fetch bcd value STA tmp :\ store as 2nd parameter ADC tmp :\ 2*tmp + carry TAY :\ save bcd value TXA :\ fetch binary value ASL :\ binary 2* BNE loop :\ 8 times, until end marker shifted out TYA CLD:RTS :\ leave with decimal mode off
\ Convert BCD to Binary \ -------------------------------------------- \ On entry, A=BCD value &00-&99 \ On exit, A=binary value 0-99 \ X, tmp corrupted .BCDtoBIN TAX :\ save low bcd digit LSR :\ high digit LSR LSR LSR :\ / 16 -> 0-9 STA tmp ASL :\ -> *2 ASL :\ -> *4 ADC tmp :\ -> *5 ASL :\ -> *10 STA tmp TXA :\ low digit AND #&0F :\ high digit masked out ADC tmp :\ final binary value RTS
