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@@ -0,0 +1,100 @@
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+#include <stdio.h>
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+#include <stdlib.h>
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+#include <stdint.h>
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+#include <stdbool.h>
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+
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+struct primes_da {
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+ uint64_t *data;
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+ uint64_t size;
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+ uint64_t cap;
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+};
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+
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+
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+bool isprime(struct primes_da *primes, uint64_t n);
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+void primes_fill(struct primes_da *primes);
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+
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+int
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+main(int argc, const char **argv)
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+{
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+ uint64_t res = 0;
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+ uint64_t i = 0;
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+ uint64_t target = 600851475143;
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+ uint64_t prime = 0;
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+ ldiv_t dm = {0};
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+ struct primes_da primes = {0};
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+
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+ primes.cap = 256;
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+ primes.data = calloc(primes.cap, sizeof(uint64_t));
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+ primes.size = 0;
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+
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+ primes_fill(&primes);
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+
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+ while ( i < target ) {
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+ if ( i >= primes.size ) {
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+ primes.cap = primes.cap * 2;
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+ primes.data = realloc(primes.data,
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+ primes.cap * sizeof(uint64_t));
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+ primes_fill(&primes);
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+ }
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+ prime = primes.data[i];
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+ dm = ldiv((int64_t)target, (int64_t)prime);
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+ if ( isprime(&primes, (uint64_t)dm.quot) ) {
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+ if ( prime > res ) {
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+ res = prime;
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+ }
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+ }
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+ if ( dm.rem != 0 ) {
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+ ++i;
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+ continue;
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+ }
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+ if ( prime > res ) {
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+ res = prime;
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+ }
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+ target = (uint64_t)dm.quot;
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+ }
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+
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+ printf("Result = %ld!\n", res);
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+ (void) argc; (void) argv;
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+ return 0;
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+}
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+
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+bool
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+isprime(struct primes_da *primes, uint64_t n)
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+{
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+ uint64_t i = 0;
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+ if ( (n & 1) == 0 ) {
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+ return false;
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+ }
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+
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+ if ( primes != NULL ) {
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+ if ( n < primes->data[primes->size-1] ) {
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+ for ( i = 0; i < primes->size; ++i ) {
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+ if ( n == primes->data[i] ) {
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+ return true;
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+ }
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+ }
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+ return false;
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+ }
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+ }
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+
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+ for ( i = 2; i < n; ++i ) {
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+ if ( (n % i) == 0 ) {
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+ return false;
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+ }
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+ }
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+ return true;
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+}
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+
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+void
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+primes_fill(struct primes_da *primes)
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+{
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+ uint64_t i = primes->size;
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+ if ( i == 0 ) {
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+ i = 2;
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+ }
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+ for ( ; primes->size < primes->cap; ++i ) {
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+ if ( isprime(NULL, i) ) {
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+ primes->data[primes->size++] = i;
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+ }
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+ }
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+}
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