69 lines
1.5 KiB
Plaintext
69 lines
1.5 KiB
Plaintext
// Public domain / CC0. Use freely for any purpose. RoyR 2026
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// primes.cm - Prime number calculator
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// Demonstrates: algorithms, loops, mathematical operations
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void printf(uint8 *fmt);
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int32 is_prime(int32 n) {
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if (n <= 1) return 0;
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if (n <= 3) return 1;
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if (n % 2 == 0 || n % 3 == 0) return 0;
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int32 i = 5;
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while (i * i <= n) {
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if (n % i == 0 || n % (i + 2) == 0) {
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return 0;
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}
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i = i + 6;
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}
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return 1;
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}
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int32 nth_prime(int32 n) {
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if (n == 1) return 2;
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int32 count = 1;
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int32 candidate = 3;
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while (count < n) {
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if (is_prime(candidate)) {
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count = count + 1;
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}
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candidate = candidate + 2;
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}
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return candidate - 2;
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}
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int32 count_primes_under(int32 limit) {
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int32 count = 0;
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for (int32 i = 2; i < limit; i = i + 1) {
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if (is_prime(i)) {
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count = count + 1;
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}
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}
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return count;
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}
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int32 main(void) {
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printf("First 20 prime numbers:\n");
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for (int32 i = 1; i <= 20; i = i + 1) {
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printf("%d ", nth_prime(i));
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if (i % 10 == 0) printf("\n");
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}
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printf("\n");
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int32 limit = 100;
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int32 count = count_primes_under(limit);
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printf("\nThere are %d primes less than %d\n", count, limit);
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printf("\nPrime check:\n");
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int32 test_nums[8] = { 1, 2, 15, 17, 97, 100, 101, 121 };
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for (int32 i = 0; i < 8; i = i + 1) {
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int32 num = test_nums[i];
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printf(" %d is %s\n", num, is_prime(num) ? "prime" : "not prime");
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}
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return 0;
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}
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