Re: A86: 16-bit Rotations

To: assembly-86@lists.ticalc.org
Subject: Re: A86: 16-bit Rotations
From: ComAsYuAre@aol.com
Date: Thu, 21 Sep 2000 22:17:41 EDT
Reply-To: assembly-86@lists.ticalc.org

In a message dated 9/21/00 9:21:35 PM Eastern Daylight Time, 
krevinek@yahoo.com writes:

> Wow, you guys could probably teach me a couple things about having 
>  optimized code. However I am curious as to the naming convention. I 
>  do know it is Rotation Left/Right <Something> HL, but why the 'C'? Is 
>  it because it is accessed using call instead of jmp or jsr?

rlc and rrc are rotate left carry and rotate right carry.  This is different 
from rl (rotate left) and rr (rotate right) in that rl and rr shift the 
previous carry into the vacant bit whereas rlc and rrc shift the 0th or 7th 
bit not only into the carry but also into the vacant bit.  I realize this 
isn't a very good explanation, but that's what they do...

 ;carry=0
 ld a,%10111110
 rl a
 ;a=%01111100

 ;carry=1
 ld a,%10111110
 rl a
 ;a=%01111101       ;<-- bit 0 is the carry

 ;carry is irrelevant
 ld a,%10111110
 rlc a
 ;a=%01111101       <-- bit 0 is previous bit 7

----
Jonah Cohen
<ComAsYuAre@aol.com>
http://jonah.ticalc.org

Follow-Ups:

Re: A86: 16-bit Rotations

From: Adam Thayer <krevinek@yahoo.com>