mirror of https://github.com/irmen/prog8.git
51 lines
1.2 KiB
Lua
51 lines
1.2 KiB
Lua
%import textio
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%zeropage basicsafe
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; Note: this program can be compiled for multiple target systems.
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main {
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bool[256] sieve
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ubyte candidate_prime = 2 ; is increased in the loop
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sub start() {
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sys.memset(sieve, 256, 0) ; clear the sieve
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; calculate primes
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txt.print("prime numbers up to 255:\n\n")
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ubyte amount=0
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repeat {
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ubyte prime = find_next_prime()
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if prime==0
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break
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txt.print_ub(prime)
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txt.print(", ")
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amount++
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}
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txt.nl()
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txt.print("number of primes (expected 54): ")
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txt.print_ub(amount)
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txt.nl()
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}
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sub find_next_prime() -> ubyte {
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while sieve[candidate_prime] {
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candidate_prime++
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if candidate_prime==0
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return 0 ; we wrapped; no more primes available in the sieve
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}
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; found next one, mark the multiples and return it.
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sieve[candidate_prime] = true
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uword multiple = candidate_prime
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while multiple < len(sieve) {
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sieve[lsb(multiple)] = true
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multiple += candidate_prime
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}
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return candidate_prime
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}
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}
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