prog8/examples/test.p8

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%import textio
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%import test_stack
%zeropage basicsafe
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; Note: this program is compatible with C64 and CX16.
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main {
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ubyte[256] sieve
ubyte candidate_prime = 2 ; is increased in the loop
sub start() {
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sys.memset(sieve, 256, false) ; clear the sieve, to reset starting situation on subsequent runs
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; 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()
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; test_stack.test()
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}
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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
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while multiple < len(sieve) {
sieve[lsb(multiple)] = true
multiple += candidate_prime
}
return candidate_prime
}
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}