Author Topic: Constructive and Creative uses of RLD and RRD  (Read 8760 times)

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Offline ralphdspam

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Constructive and Creative uses of RLD and RRD
« on: August 25, 2011, 09:06:44 pm »
I saw the topic "Constructive and Creative uses of IX and IY," and I liked the idea of brainstorming creative uses for commands. 

Two commands that always perplex me are RLD and RRD.  I cannot think of many practical uses of them. 
ld a, 0
ld a, a

Offline calc84maniac

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Re: Constructive and Creative uses of RLD and RRD
« Reply #1 on: August 25, 2011, 11:11:00 pm »
I use one of those in TI-Boy to emulate the SWAP (HL) instruction, which swaps the upper and lower nibbles of (HL).
It works like ld a,(hl) \ rrd.
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Offline DrDnar

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Re: Constructive and Creative uses of RLD and RRD
« Reply #2 on: August 26, 2011, 02:20:18 am »
As far as I can tell, the instructions are intended for use with BCD. They appear to allow multiplying and dividing by ten. Or sixteen, if you're using binary.
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Re: Constructive and Creative uses of RLD and RRD
« Reply #3 on: August 26, 2011, 03:12:08 pm »
Indeed, the only time I've ever used it was for BCD. It's useful if you need to recover a number from TI's floating points. For instance:

Code: [Select]
turnTheEntireOp1ToADecimalStringRegardlessOfSignificateFigures:
ld hl, op1+2
ld c, 7
outerLoop:
ld b, 2
innerLoop:
ld a, $30
rld
ld (de), a
inc de
djnz innerLoop
inc hl
dec c
jr nz, outerLoop
xor a
ld (de), a
ret
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Offline ralphdspam

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Re: Constructive and Creative uses of RLD and RRD
« Reply #4 on: August 26, 2011, 06:01:52 pm »
I'm glad there are actually uses for that command.  I like the idea of manipulating nibbles, but I don't like the fact that it modifies the source data.  Can you use it on ROM code without any problems? 
ld a, 0
ld a, a

Offline calcdude84se

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Re: Constructive and Creative uses of RLD and RRD
« Reply #5 on: August 26, 2011, 09:01:12 pm »
I'm glad there are actually uses for that command.  I like the idea of manipulating nibbles, but I don't like the fact that it modifies the source data.  Can you use it on ROM code without any problems? 
You probably shouldn't be manipulating code by nibble :P Anyway, A contains the correct result even if (HL) can't be changed, IIRC.
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Offline calc84maniac

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Re: Constructive and Creative uses of RLD and RRD
« Reply #6 on: August 26, 2011, 10:30:15 pm »
* calc84maniac uses OPTIMIZATION
Code: [Select]
turnTheEntireOp1ToADecimalStringRegardlessOfSignificateFigures:
ld hl, op1+2
ld b, 7
ld a, $30
loop:
rld
ld (de), a
inc de
rld
ld (de), a
inc de
inc hl
djnz loop
xor a
ld (de), a
ret

Edit:
Ooh, even better!
Code: [Select]
turnTheEntireOp1ToADecimalStringRegardlessOfSignificateFigures:
ld hl, op1+2
ld bc, 7
loop:
ld a, $33
rrd
ldi
ld (de), a
inc de
jp pe, loop
xor a
ld (de), a
ret
« Last Edit: August 26, 2011, 10:40:08 pm by calc84maniac »
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Offline Xeda112358

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Re: Constructive and Creative uses of RLD and RRD
« Reply #7 on: December 30, 2011, 11:40:38 pm »
Ooh, rrd and rld are some of my favorite instructions! When I was describing what it does in my pocket asm tutorial was this:
Quote
rrd/rld the two nibbles from (hl) and the last nibble of 'a' make three nibbles. rrd                
           rotates them right and rld rotates them left.
As for a way to use them, I have a few codes that make excellent use of them. This one is from my program BSPRT. It uses hexadecimal sprite data, so instead of converting the hex string to a location in RAM and then copying it to the screen, I just did both at once (here is the sprite display part):
Code: (BSPRT) [Select]
;Inputs:
;     HL points to the buffer location to draw to
;     DE points to the sprite data

     ld bc,080Ch     ;010C08
Loop:
     call PutNibble  ;CD****
     call PutNibble  ;CD****
     ld a,b          ;78
     ld b,0          ;0600
     add hl,bc       ;09
     ld b,a          ;47
     djnz Loop       ;10F3
     ret             ;C9
PutNibble:
     ld a,(de)       ;1A
     add $C0         ;C6C0
     jr nc,$+4       ;3002
       sub 7         ;D607
     rld             ;ED6F
     inc de          ;13
     ret             ;C9
This is my favorite one, though. When I made a graph shifting routine, I made these to shift 4 pixels very quickly:
Code: [Select]
ShiftLeft4:
     ld hl,GraphBuf+767
     ld c,64
       xor a
       ld b,12
         rld
         dec hl
         djnz $-3
       dec c
       jr nz,$-9
       ret
Code: [Select]
ShiftRight4:
     ld hl,GraphBuf
     ld c,64
       xor a
       ld b,12
         rrd
         inc hl
         djnz $-3
       dec c
       jr nz,$-9
       ret
I feel pretty proud of these :) I think the first can be optimised more, but it is still nice, I think :)

Offline chickendude

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Re: Constructive and Creative uses of RLD and RRD
« Reply #8 on: December 31, 2011, 05:32:36 am »
Unless i'm missing something, the first just says "Array", maybe you pasted the wrong thing?

Offline Hayleia

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Re: Constructive and Creative uses of RLD and RRD
« Reply #9 on: December 31, 2011, 06:49:29 am »
It is because she wrote [code=something].
Here is what she meant :)

Code: [Select]
;Inputs:
;     HL points to the buffer location to draw to
;     DE points to the sprite data

     ld bc,080Ch     ;010C08
Loop:
     call PutNibble  ;CD****
     call PutNibble  ;CD****
     ld a,b          ;78
     ld b,0          ;0600
     add hl,bc       ;09
     ld b,a          ;47
     djnz Loop       ;10F3
     ret             ;C9
PutNibble:
     ld a,(de)       ;1A
     add $C0         ;C6C0
     jr nc,$+4       ;3002
       sub 7         ;D607
     rld             ;ED6F
     inc de          ;13
     ret             ;C9
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Offline Xeda112358

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Re: Constructive and Creative uses of RLD and RRD
« Reply #10 on: December 31, 2011, 10:21:06 am »
Unless i'm missing something, the first just says "Array", maybe you pasted the wrong thing?
I am not seeing that... On mine, Hayleia and I have the same thing...

Offline Hayleia

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Re: Constructive and Creative uses of RLD and RRD
« Reply #11 on: December 31, 2011, 10:23:43 am »
Unless i'm missing something, the first just says "Array", maybe you pasted the wrong thing?
I am not seeing that... On mine, Hayleia and I have the same thing...
??? I see "Array" too on yours. Maybe it depends on the browser.
But do you see "BSPRT" next to "code" ? (I don't see it, I had to quote you to see it should be here ;))
« Last Edit: January 02, 2012, 12:27:43 pm by Hayleia »
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Offline chickendude

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Re: Constructive and Creative uses of RLD and RRD
« Reply #12 on: December 31, 2011, 11:00:35 am »
Well, it doesn't really matter now as i see what code you were talking about in Hayleia's post. Btw, what exactly do you mean by "hexidecimal sprites"? I'm trying to figure out what exactly your code does.

Offline Xeda112358

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Re: Constructive and Creative uses of RLD and RRD
« Reply #13 on: December 31, 2011, 02:10:01 pm »
Ah, well with that code, will draw a sprite with hexadecimal data input. By that, I mean . db "3C4281818181423C" as opposed to .db 3Ch,42h,81h,81h,81h,81h,42h,3Ch

The first is what a TI-BASIC string would be like and the program that code is in is designed for TI-BASIC programmers to use.

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Re: Constructive and Creative uses of RLD and RRD
« Reply #14 on: January 02, 2012, 06:07:01 am »
Axe uses RRD and RLD for nibble storing.  I've never used them anywhere else, they are definitely very uncommon.  :ninja:

Code: [Select]
;hl = Nth nibble after address $8000
;e = Nibble to store there
NibSto:
scf
rr h
rr l
jr nc,__NibStoHigh
rrd
ld a,e
rld
ret
__NibStoHigh:
rld
ld a,e
rrd
ret
__NibStoEnd:
« Last Edit: January 02, 2012, 06:07:40 am by Quigibo »
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