A86: Re: Re: divide by 2

To: <assembly-86@lists.ticalc.org>
Subject: A86: Re: Re: divide by 2
From: "Eugene Dirks" <e1066@sherbtel.net>
Date: Wed, 3 Mar 1999 22:09:14 -0600
Delivered-To: assembly-86-outgoing@towerguard.unix.edu.sollentuna.se
Delivered-To: assembly-86@lists.ticalc.org
Reply-To: assembly-86@lists.ticalc.org


thanks, I was worried it was something easy like that.  Binary is one of
those things that I know i should learn better, but until now I just haven't
had any motivation to do so
    ,billybobIV
    chad@dirks.com
    http://chad.dirks.com


----- Original Message -----
From: David Phillips <david@acz.org>
To: <assembly-86@lists.ticalc.org>
Sent: Wednesday, March 03, 1999 5:45 PM
Subject: A86: Re: divide by 2


>
>Hehe, that's a "classic" newbie question.  If you're talking floating
point,
>just use the call...
>
>_FPDIV -- divide OP1 by OP2
>
>For registers, this is very simple.  Think in binary when you program.  If
>you shift a binary number left, it's multiplied by two.  If you shift it
>right, it's...drumroll...divided by two...
>
>  ld a,5
>  or a    ; clear carry flag (probably not needed)
>  rra     ; divide by two!!!
>
>  ld c,17
>  srl c   ; divide by two
>
>  ld b,5
>  sra b  ; multiply by two
>
>  ld a,78
>  rra     ; divide by 8
>  rra
>  rra
>  and %00011111    ; mask off excess bits
>
>If you're using A, you can use <rla> and <rra>, which is good because
>they're one byte, 4 t-state instructions.  Just remember that the carry
flag
>is rotated into the other end, so if you are doing multiple shifts, you
will
>probably have to mask off (AND) the extra bits.  <sra> and <srl> can be
used
>with any register and set the other bit to 0 (which you want), but take up
>two bytes and 8 t-states (twice an RLA or RRA).
>
>>

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