prog8/examples/primes.p8

54 lines
1.3 KiB
Lua

%import textio
%zeropage basicsafe
; Note: this program can be compiled for multiple target systems.
main {
bool[256] sieve
ubyte candidate_prime = 2 ; is increased in the loop
sub start() {
sys.memset(sieve, 256, 0) ; clear the sieve, to reset starting situation on subsequent runs
; calculate primes
txt.print("prime numbers up to 255:\n\n")
ubyte amount=0
repeat {
ubyte prime = find_next_prime()
if prime==0
break
txt.print_ub(prime)
txt.print(", ")
amount++
}
txt.nl()
txt.print("number of primes (expected 54): ")
txt.print_ub(amount)
txt.nl()
; test_stack.test()
}
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
}
}