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@label mul
; multiply a signed/unsigned (a) and an unsigned number (b)
; parameters RA = a
; RB = b
; return RG = a * b
stack_stash RA RB
; initialize return value in RG to 0
ldi 0 RG
@label mul_loop
; if b == 0, we are done
subi RB 0 RB
bri zero mul_done
; RG += RA
add RA RG RG
dec RB
jpi mul_loop
@label mul_done
stack_restore RA RB
return
; Recursive impl of the factorial
; Calling convention is that arguments are in registers RA..RG (max 7 arguments since RH = SP)
; and the return value is in RG (note: overwriting arg in RG)
@label fact
; parameters RA = n
; return RG = factorial(n)
subi RA 0 RA
bri zero fact_basecase
@label fact_reccase
stack_stash RA RB
mov RA RB ; RB := n
subi RA 1 RA ; RA := n - 1
calli fact ; RG := fact(n - 1)
mov RG RA ; RA := fact(n - 1)
calli mul ; RG := n * fact(n - 1)
stack_restore RA RB
return
@label fact_basecase
ldi 1 RG
return
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