I'm trying to generate pseudo random numbers 1-255(yes zero is a special
case). Following Graphic Gems, and code I found at codebase64 I came up
with this:

ORG $300

LDY #$00

XOR LSR RAND
LDA RAND
BCC SKIP
EOR #$B8
SKIP STA RAND
STA $2000,Y
INY
BEQ DONE
JMP XOR

DONE RTS

RAND DB $01

I then put the values in text file:

10 D$ = CHR$ (4)
20 PRINT D$;"OPEN RAND"
30 PRINT D$;"WRITE RAND"
40 FOR I = 0 TO 255
50 PRINT PEEK (8196 + I)
60 NEXT
70 PRINT D$;"CLOSE"

Pasted them into a spreadsheet and sorted. It doesn't work. There are
missing numbers, duplicate numbers. What am I doing wrong? Is there a
better method?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <vbb26i$1tf0$[email protected]>, Duhast <[email protected]> wrote: >I'm trying to generate pseudo random numbers 1-255(yes zero is a special >case). Following Graphic Gems, and code I found at codebase64 I came up

with this:

ORG $300

LDY #$00

XOR LSR RAND
LDA RAND
BCC SKIP
EOR #$B8
SKIP STA RAND
STA $2000,Y
INY
BEQ DONE
JMP XOR

DONE RTS

RAND DB $01

I then put the values in text file:

10 D$ = CHR$ (4)
20 PRINT D$;"OPEN RAND"
30 PRINT D$;"WRITE RAND"
40 FOR I = 0 TO 255
50 PRINT PEEK (8196 + I)
60 NEXT
70 PRINT D$;"CLOSE"

Pasted them into a spreadsheet and sorted. It doesn't work. There are >missing numbers, duplicate numbers. What am I doing wrong? Is there a >better method?

You should use PEEK(8192+I). That may be the only problem.

And you can optimize the routine a bit:

LOOP LDA RAND
LSR
BCC SKIP
EOR #$B8
SKIP STA RAND
STA $2000,Y
INY
BNE LOOP
RTS

You don't have to save RAND in a memory location at all, just remove the
LDA RAND and STA RAND. It's important for LFSR to start at a non-0 number
(if you start it with 0, it stays at 0), so I'd initialize RAND to 1 before
the loop.

LDA #1
STA RAND

You can see it works with a more elaborate code which counts the occurrence
of each byte at output:

LDY #0
LDA #0
CLR STA $4000,Y
INY
BNE CLR
LDA #1
LOOP LSR
BCC SKIP
EOR #$b8
SKIP TAX
INC $4000,X
INY
BNE LOOP
RTS

Where $4000-40ff will have $01 in every position except $4000, and $40B8 will have $02 (something had to occur twice since $00 is not an output).

Kent

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 9/5/2024 4:13 PM, Kent Dickey wrote:

You should use PEEK(8192+I). That may be the only problem.

Ok, it was a brain fart of 4096 vs 8192, and that was corrected, but I
still get bad numbers.

I was running Applewin, and it gives me one set of numbers, with missing
ones and duplicates. I ran it under GSplus, and it gave me different
numbers, but no missing and one duplicate(but I think I know
why(executing loop an extra round)), I then ran it on real //gs hardware
and it matches the GSplus output.

Shouldn't it always generate the same sequence with the same seed? Does
the EOR function not work right on a 6502 vs 65816, or is Applewin not
right?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

In article <vbr0q9$3ddnt$[email protected]>, Duhast <[email protected]> wrote: >On 9/5/2024 4:13 PM, Kent Dickey wrote:

You should use PEEK(8192+I). That may be the only problem.

Ok, it was a brain fart of 4096 vs 8192, and that was corrected, but I
still get bad numbers.

I was running Applewin, and it gives me one set of numbers, with missing
ones and duplicates. I ran it under GSplus, and it gave me different >numbers, but no missing and one duplicate(but I think I know
why(executing loop an extra round)), I then ran it on real //gs hardware
and it matches the GSplus output.

Shouldn't it always generate the same sequence with the same seed? Does
the EOR function not work right on a 6502 vs 65816, or is Applewin not
right?

Your original code didn't initialize RAND to anything. So it may vary
between systems. My modified code initialized it to 1.

Kent

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

On 9/11/2024 11:58 PM, Kent Dickey wrote:

Your original code didn't initialize RAND to anything. So it may vary between systems. My modified code initialized it to 1.

Kent

In my original code, I DB'd RAND as $01. I'm not great at assembly, but
is that not initializing it?

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)

Duhast wrote:

On 9/11/2024 11:58 PM, Kent Dickey wrote:

Your original code didn't initialize RAND to anything. So it may vary
between systems. My modified code initialized it to 1.

Kent

In my original code, I DB'd RAND as $01. I'm not great at assembly, but
is that not initializing it?

If your assembler takes DB to mean "define a byte within the assembled
object code," then yes. Use the Monitor to check your program after you load
it into RAM, but before you execute it, to verify it is $01.

--
]DF$
The New Apple II User's Guide:
https://macgui.com/newa2guide/

--- SoupGate-Win32 v1.05
* Origin: fsxNet Usenet Gateway (21:1/5)