prog8/examples/primes.p8
2020-03-14 18:11:38 +01:00

62 lines
1.4 KiB
Lua

%import c64utils
%zeropage basicsafe
main {
ubyte[256] sieve
ubyte candidate_prime = 2 ; is increased in the loop
sub start() {
memset(sieve, 256, false) ; clear the sieve, to reset starting situation on subsequent runs
; calculate primes
c64scr.print("prime numbers up to 255:\n\n")
ubyte amount=0
forever {
ubyte prime = find_next_prime()
if prime==0
break
c64scr.print_ub(prime)
c64scr.print(", ")
amount++
}
c64.CHROUT('\n')
c64scr.print("number of primes (expected 54): ")
c64scr.print_ub(amount)
c64.CHROUT('\n')
check_eval_stack()
}
sub find_next_prime() -> ubyte {
while sieve[candidate_prime] {
candidate_prime++
if candidate_prime==0
return 0 ; we wrapped; no more primes available in the sieve
}
; found next one, mark the multiples and return it.
sieve[candidate_prime] = true
uword multiple = candidate_prime
while multiple < len(sieve) {
sieve[lsb(multiple)] = true
multiple += candidate_prime
}
return candidate_prime
}
sub check_eval_stack() {
if X!=255 {
c64scr.print("stack x=")
c64scr.print_ub(X)
c64scr.print(" error!\n")
}
}
}