Finonacci numbers

#!/boot/system/bin/yab
//******************* ProgrammVerzeichnis bestimmen ************************************
n=30
print time$
print fib2(n)
print time$
sub fib2(n)
if(n<2)then
return n
endif
n=fib2(n-2) + fib2(n-1)
return n
end sub

print "-----------------"
n=30
print time$
print fibonacci (n)
print time$
sub fibonacci (n)
n1 = 0
n2 = 1
for k = 1 to abs(n)
sum = n1 + n2
n1 = n2
n2 = sum
next k
if n < 0 then
return n1 * ((-1) ^ ((-n) + 1))
else
return n1
end if
end sub