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2015-10-11 07:18

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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2015-10-21 06:36

Bitbreaker

Registered: Oct 2002
Posts: 508

If you want it comfortable, switch to Java.

2015-10-21 13:44

Rastah Bar
Account closed

Registered: Oct 2012
Posts: 336

If you want to make it a subroutine, is this a good idea?

start:  lda zp2
        clc
        ldx #$60
        rol zp1
        rol zp2
        sbx #$00
        lda $c000,x
        sta start+2
        rts

Where $c000, $c020, $c040, and $c060 contain $18,$38,$38,$18, respectively (opcode clc=$18, sec=$38).

First call: jsr init
Subsequent calls: jsr start

With RLA:

 
start:
        clc
        lda #$60
        rol zp1
        rla zp2
        tax
        lda $c000,x
        sta start
        rts

But I can imagine you want to call it for example 8 times in a row to generate an entire byte in which case the overhead of storing the state of the MLS generator can be much reduced.

2015-10-21 16:29

Oswald

Registered: Apr 2002
Posts: 5095

Quote: If you want it comfortable, switch to Java.

2015-10-22 09:30

Rastah Bar
Account closed

Registered: Oct 2012
Posts: 336

Quoting Color Bar

If you want to make it a subroutine, is this a good idea?

start: lda zp2 clc ldx #$60 rol zp1 rol zp2 sbx #$00 lda $c000,x sta start+2 rts

Where $c000, $c020, $c040, and $c060 contain $18,$38,$38,$18, respectively (opcode clc=$18, sec=$38).

[/code]

Faster is:

init:  lda #seed1
       sta zp1
start: lda #seed2
       clc ; or sec depending on how you want to initialize
       rol zp1
       rol
       sta start+1
       tax
       lda $c000,x
       sta start+2
       rts

This requires a look up table with $18,$38 values for any value of A after the rol. This has the advantage that it is easier to generalize to other MLS orders, where you may have to EOR more than two bits. No UOC required :-(

2015-10-25 12:50

Monte Carlos

Registered: Jun 2004
Posts: 364

lax blabla,x (y)
sbx #..

should emulate cpx,y or cpx,x

2015-10-25 16:19

chatGPZ

Registered: Dec 2001
Posts: 11390

but since that destroys akku, you can just aswell use