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John West
PostPosted: Thu Jan 17, 2019 10:11 am 
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Joined: Tue Sep 03, 2002 12:58 pm
Posts: 325
I don't know what I was dreaming last night, but this came to me just as I was waking up:

Add two 16 bit numbers, using no instruction more than once. Different addressing modes count as the same instruction.
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BitWise
PostPosted: Thu Jan 17, 2019 11:03 am 
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Joined: Tue Mar 02, 2004 8:55 am
Posts: 996
Location: Berkshire, UK
How about?
Code:
 ldx #1
 clc
.loop
 lda A,x
 adc B,x
 sta R,x
 dex
 bpl .loop

Does 'using no instruction more than once' mean only once in the source or only once during execution?

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6502 & PIC Stuff - http://www.obelisk.me.uk/
Cross-Platform 6502/65C02/65816 Macro Assembler - http://www.obelisk.me.uk/dev65/
Open Source Projects - https://github.com/andrew-jacobs
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John West
PostPosted: Thu Jan 17, 2019 11:54 am 
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Posts: 325
Only once in the source is fine. Only once during execution is a little more of a challenge. Using 65816 instructions is considerably less of a challenge :-)
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drogon
PostPosted: Thu Jan 17, 2019 12:07 pm 
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Joined: Wed Feb 14, 2018 2:33 pm
Posts: 1467
Location: Scotland
Code:

r0 = $80
r1 = $82
; 6502 code to put numbers into r0, r1
jsr sweet16
add r1
rtn
; result is in r0


-Gordon

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Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/
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rwiker
PostPosted: Thu Jan 17, 2019 12:14 pm 
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Joined: Thu Mar 03, 2011 5:56 pm
Posts: 284
6502 or 65C02 instruction set?
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rwiker
PostPosted: Thu Jan 17, 2019 12:40 pm 
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Joined: Thu Mar 03, 2011 5:56 pm
Posts: 284
I came up with this:

Code:

lda Op2
eor #$ff
sta Res
ldx Op1
txa
clc
sbc Res
tax
stx Res
ldy Op1+1
tya
adc Op2+1
tay
sty Res+1
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John West
PostPosted: Thu Jan 17, 2019 1:08 pm 
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Joined: Tue Sep 03, 2002 12:58 pm
Posts: 325
That's quite similar to my one:
Code:
CLC
LDA a
ADC b
STA result
LDX b+1
TXA
EOR #$FF
TAX
STX tmp
LDY a+1
TYA
SBC tmp
TAY
STY result+1
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