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BitWise
PostPosted: Sat Nov 02, 2019 7:46 pm 
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Joined: Tue Mar 02, 2004 8:55 am
Posts: 996
Location: Berkshire, UK
Addition and subtraction are easy enough. Work from the least significant byte to the most.
Code:
; C = A + B
clc
lda a0
adc b0
sta c0
lda a1
adc b1
sta c1
lda a2
adc b2
sta c2
lda a3
adc b3
sta c3

; C = A - B
sec
lda a0
sbc b0
sta c0
lda a1
sbc b1
sta c1
lda a2
sbc b2
sta c2
lda a3
sbc b3
sta c3

Check the code library for multiply and divide algorithms.

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Andrew Jacobs
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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Chromatix
PostPosted: Sat Nov 02, 2019 11:44 pm 
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Joined: Mon May 21, 2018 8:09 pm
Posts: 1462
It really is the same as working out sums by hand - only the "digits" count up to 255 instead of only to 9.
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