21 Jan
2008
21 Jan
'08
6:29 p.m.
Date: Sun, 20 Jan 2008 20:57:27 -0800
From: Brent Hilpert <hilpert at cs.ubc.ca>
Subject: Re: div by 10 on Z80 was RE: Reading Polymorphic ---
(I expect you may have noticed already..) the
subroutine (div10s) is
only called once now, you could inline it to save another 4 bytes.
You can do a bit better with that and by using the carryout to form
the quotient bits:
div10:
xor a
ld de,0fd80h ; largest power of 2 times 10 less then 800d
ld b,07 ; only seven loops needed to finish divide 80
divloop:
add hl,de ; trial subtract
jr c,div10s1 ; carry means trial passed
sbc hl,de ; undo previous add, carry is clear
div10s1:
rl a
add hl,hl ; shift number to reuse same constant, 640 decimal
djnz divloop
add hl,hl ; push full remainder in HL
ret
Again, I haven't tried it out, but it should work.
Cheers,
Chuck