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Add example routine finding min among 3 numbers.

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Radosław Kujawa 2018-04-05 00:32:53 +02:00
parent 7cf3f263e3
commit b44dcdc91a
1 changed files with 28 additions and 0 deletions
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; min3
; Takes 3 numbers (A, B, C), passed on stack, finds the minimum.
; Result is also passed on stack. Assumes it is being called via jsr.
.set retl,0x10
.set reth,0x11
.set res,0x12
min3: pla ; pull low byte of return address
sta retl
pla
sta reth
pla ; pull C from stack
sta res ; save C into res
pla ; pull B from stack
cmp res ; compare B and C
bpl bltc ; branch if B > C
sta res ; if C is smaller, save it to res
bltc: pla ; pull A from stack
cmp res ; compare A and whatever is in res
bpl ret ; branch if A > res
sta res ; otherwise save A to res
ret: lda res ; load res into accumulator
pha ; save to the stack
lda reth ; restore return address
pha
lda retl
pha
rts ; return from function