103 lines
2.0 KiB
C
103 lines
2.0 KiB
C
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#ifdef MCC
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#define NULL 0
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#else
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#include <stdio.h>
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#include <stdlib.h>
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#endif
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int main (int argc, char **argv)
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{
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if (argc!=2)
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{
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fprintf (stderr, "Usage: ./sieve <n>\ncalcule et affiche les nombres premiers inferieurs a <n>.\n");
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fflush (stderr);
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exit (10); /* non mais! */
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}
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{
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int n;
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int *bits;
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n = atoi (argv[1]); // conversion chaine -> entier.
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if (n<2)
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{
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fprintf (stderr, "Ah non, quand meme, un nombre >=2, s'il-vous-plait...\n");
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fflush (stderr);
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exit (10);
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}
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bits = malloc (8*n); // allouer de la place pour n entiers (booleens).
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// Ca prend 32 fois trop de place. Mais C-- n'a pas les operations &, |,
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// qui nous permettraient de manipuler des bits individuellement...
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if (bits==NULL)
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{
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fprintf (stderr, "%d est trop gros, je n'ai pas assez de place memoire...\n");
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fflush (stderr);
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exit (10);
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}
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zero_sieve (bits, n);
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bits[0] = bits[1] = 1;
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fill_sieve (bits, n);
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print_sieve (bits, n);
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free (bits); // et on libere la place memoire allouee pour bits[].
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}
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return 0;
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}
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int zero_sieve (int *bits, int n)
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{
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int i;
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for (i=0; i<n; i++)
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bits[i] = 0;
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return 0;
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}
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int fill_sieve (int *bits, int n)
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{
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int last_prime;
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for (last_prime = 2; last_prime<n; )
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{
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cross_out_prime (bits, n, last_prime);
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while (++last_prime<n && bits[last_prime]);
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}
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return 0;
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}
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int cross_out_prime (int *bits, int n, int prime)
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{
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int delta;
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for (delta = prime; (prime = prime + delta) < n; )
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bits[prime] = 1;
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return 0;
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}
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int print_sieve (int *bits, int n)
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{
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char *delim;
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int i;
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int k;
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char *buf;
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printf ("Les nombres premiers inferieurs a %d sont:\n", n);
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delim = " ";
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k = 0;
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for (i=0; i<n; i++)
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{
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if (bits[i]==0)
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{
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printf ("%s%8d", delim, i);
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if (++k>=4)
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{
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printf ("\n"); // retour à la ligne.
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k = 0;
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delim = " ";
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}
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else
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printf (" "); // espace.
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}
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}
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fflush (stdout); // on vide le tampon de stdout, utilise par printf().
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return 0;
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}
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