Subject: RE: Subject: Re: div by 10 on Z80

[dwight elvey]

> From: cclist at sydex.com
> To: cctalk at classiccmp.org
> Date: Wed, 23 Jan 2008 09:31:50 -0800
> Subject: Subject: RE: Subject: Re: div by 10 on Z80
>
>> Date: Tue, 22 Jan 2008 19:33:15 -0800
>> From: dwight elvey 
>
>> Here goes with using your idea to double use the a register. Except
>> If I start it with 2, I can use the carry instead of the sign bit. What
>> fun!
>>
>> Div10:
>> ld a,#2
>> ld de,#-640d
>> divloop:
>> add hl,de
>> jr c, div1
>> sbc hl,de
>> div1:
>> rl a
>> jr nc,divloop
>> add hl,hl
>> ret
>
> Ah, but you forgot the add hl,hl to shift the dividend after each
> iteration. Put it at the top of the loop so it doesn't interfere
> with the operation of the "rl a/jr nc" pair and scale your divisor by
> an additional power of 2 and you should have it.

Hi Chuck
 See my other post. I realized the missing 'add hl,hl'. As you
can see, I moved this to the front of the loop and increased
the value of DE to -1280. This allowed the use of the bit
in the a register!!

>
> By now, we've probably bored the hardware guys to tears and DEC
> people are tearing out their hair, so we should probably drop the
> subject.

 I think there is still some interest in coding tricks. Even if they
are using DEC machines.
Dwight




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