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BillG
PostPosted: Sat Aug 22, 2020 12:32 pm 
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Joined: Thu Mar 12, 2020 10:04 pm
Posts: 702
Location: North Tejas
dmsc wrote:
This is smaller and faster, without using any temporary:
Code:
        lda     W_      ; 4
        asl             ; 2
        tax             ; 2
        lda     W_+1    ; 4
        rol             ; 2
        tay             ; 2

        txa             ; 2
        clc             ; 2
        adc     S_      ; 4
        sta     W_      ; 4

        bit     S_      ; 4
        bpl     l2      ; 2  3

        dey             ; 2  -
l2:
        bcc      l3     ; 2  3
        iny             ; 2  -
l3:
        sty     W_+1    ; 4   



I'm sorry, I should not have been so lazy. The intent was not to add to the sum of W and W, but to test how the compiler handled adding a signed byte to a sixteen-bit value already in registers.
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