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Monte Carlos
Registered: Jun 2004
Posts: 364 |
Event id #2417 : First CSDb "Unintended OpCode coding challenge"
So here it is. The First CSDb "Unintended OpCode coding challenge" starts over.
First CSDb "Unintended OpCode Coding Challenge"
Please give some feedback about your interest in this compo.
For those who have been part of the discussion
http://csdb.dk/forums/?roomid=12&topicid=112819#112927
please let me know if you are in better agreement with the reworked rules than before.
However, there will not be a rule change anymore. |
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Bitbreaker
Registered: Oct 2002
Posts: 508 |
SRE and SLO and others can take up to 8 cycles (indirect y indexed) and are thus not necessarily faster, also i have not come across any good use for an effect for the RRA and RLA opcodes so far, though they of course would save cycles if used properly.
lda #$00
slo $xxxx
can also be expressed as:
asl label+1
label lda #$00
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Quoting Bitbreaker
lda #$00
slo $xxxx
can also be expressed as:
asl label+1
label lda #$00
Not always. |
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Monte Carlos
Registered: Jun 2004
Posts: 364 |
Thats what i tried recently:
ldx #60
fsprite lda #0
sta sprite+2,x
lda #$f0
sta sprite+1,x
lda #$ff
sta sprite+2,x
sbx #3 ; or axs #3
bpl fsprite
rts
----------------------------------
ldy # 24
ldx #0
setscreen:
lda #'*'
hi = *+2
sta screen,x
txa
sbx #$d8
bcc j
inc hi
j dey
bpl setscreen
rts
-------------------------------------
loop:
jsr waitretrace
lda #7
ldx $d016
sbx #$f9
stx $d016
jmp loop
--------------------------------------- |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Is there any concensus on the names given to the various extra instructions?
There are at least three references on codebase64:
http://codebase64.org/doku.php?id=base:extra_instructions_of_th..
http://unusedino.de/ec64/technical/aay/c64/ibmain.htm
http://www.oxyron.de/html/opcodes02.html
Which one is the most complete / commonly used?
A document by Groepaz was mentioned. Where can I find that?
I once used:
sta label+1
txa
label sbx #$00
To get X --> A and X-A --> A |
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Monte Carlos
Registered: Jun 2004
Posts: 364 |
just search for "no more secrets" and reveal:
No More Secrets
Think this and grahams reference are the most advanced docus. |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Thanks!
I constructed a 15 bit Maximum Length Sequence (MLS) generator, using RLA. This is what I have got now:
lda #seed1
sta zp1
lda #seed2
sta zp2
start:
clc
lda #$60 ;MSB of zp2 is output of the MLS, bits 6+5 are EORed (according to primitive polynomial for m=15)
rol zp1
rla zp2 ;actually the Carry flag contains the most recent output of the MLS at this point, while the MSB of zp2 is the output of the previous cycle.
beq start ; shift a zero bit in
;now we must distinguish between 01 or 10 versus 11 for bits 6 and 5 of A
eor #$60
beq start ; shift a zero bit in
sec ; shift a one bit in
jmp start+1
Reference for MLS: http://www.kempacoustics.com/thesis/node83.html
I don't know if this can be done more efficiently (probably). |
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Monte Carlos
Registered: Jun 2004
Posts: 364 |
Is this related to generation of random numbers which also are maximum length sequences or is this something on it's own? |
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Rastah Bar
Account closed
Registered: Oct 2012
Posts: 336 |
Yes, this is related. I dont know the details, but the reference explains more. I remembered something about random number generation with MLS, looked up the reference and saw a connection with RLA. |
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Monte Carlos
Registered: Jun 2004
Posts: 364 |
Interesting idea. I only know bout these eor randomizers. |
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Bitbreaker
Registered: Oct 2002
Posts: 508 |
Nice! A optimization that comes to my mind at a chort glance:
eor #$60
beq start ; shift a zero bit in
sec ; shift a one bit in
jmp start+1
;isn't that the same as:
eor #$60
cmp #$01 ;sets carry on $20 $40 $60 and clears carry on $00
bne start+1 ;branch always
The lda #$60 + eor #$60 gives me the feeling that it can be optimized too, twice the same value :-D Also it would help to get a negated carry, hmm |
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