Subj : Faster algorithm for prim numbers..!!
To   : comp.programming
From : Robert Bralic
Date : Wed Sep 21 2005 10:15 am

I weated a simple program, he is compiled
with gcc, and generates prim numbers,
with fastes method that I find.He is based
on divide with generated prim numbers...
At end he gives time report on format:
dd:hh:mi:sec...
Precompile as gcc prim.c -o prim, and use
him as "prim upper_bound",as example:
"prim 1000".If anybody have some idea
how to make algorithm fastes write to me...!!

//----------------------------------------------------------
#include<stdio.h>
#include<malloc.h>
#include<time.h>

void transform(char*, int);
struct lst{
   long int value;
   struct lst* next;
};

int main(int argc, char* argv[]){
   long int i,j,k, time_begin, time_end, razlika_vremena;
   char trans_value[20];
   struct lst *prvi, *tekuci_prvi, *tekuci_drugi, *zadnji;
   prvi=(struct lst*)malloc(sizeof(struct lst));
   prvi->next=(struct lst*)malloc(sizeof(struct lst));
   prvi->value=1;
   prvi->next->value=2;
   tekuci_prvi=prvi->next;
   zadnji=prvi->next;
   zadnji->next=(struct lst*)NULL;
   k=atoi(argv[1]);
   tekuci_drugi=prvi;
   time(&time_begin);
   for(i=1;i<k;i++){
exit:
   tekuci_drugi=prvi;
      while(tekuci_drugi->next){
         if((i%(tekuci_drugi->value)==0) && tekuci_drugi->value!=1){
            if(i==1){
            goto exit;
            }
            i++;
            goto exit;
  }
      tekuci_drugi=tekuci_drugi->next;
      }
          tekuci_prvi->next=(struct lst*)malloc(sizeof(struct lst));
          tekuci_prvi=tekuci_prvi->next;
          tekuci_prvi->value=i;
          tekuci_prvi->next=(struct lst*)NULL;
   /*printf("%ld\n",i);*/
  }
     tekuci_prvi=prvi;
     while(tekuci_prvi->next){
         printf("%d\n", tekuci_prvi->value);
         tekuci_prvi=tekuci_prvi->next;
     }
     time(&time_end);
     razlika_vremena=time_end-time_begin;
     transform(&trans_value, razlika_vremena);
     printf("\nGeneriranje i stampanje do %d broja je trajalo:%s", k,
trans_value);
     exit(0);
}




void transform(char* t, int time){
   int days, hours, minuts, seconds, i, timi;
   char dd[5],hh[3],mi[3],sec[3];
   timi=time;
   days=time/(24*3600);
   i=time%(24*3600);
   time=time/(24*3600)+i;
   hours=(time/3600);
   i=time%3600;
   time=time/3600+i;
   minuts=time/60;
   time=time/60;
   time=time%60;
   seconds=timi-days*3600*24-hours*3600-minuts*60;
   if(days<10){
      sprintf(dd,"0%d",days);
   }else{
      sprintf(dd,"%d",days);
   }
   if(hours<10){
      sprintf(hh,"0%d",hours);
   }else{
      sprintf(hh,"%d",hours);
   }
   if(minuts<10){
      sprintf(mi,"0%d",minuts);
   }else{
      sprintf(mi,"%d",minuts);
   }
   if(seconds<10){
      sprintf(sec,"0%d",seconds);
   }else{
      sprintf(sec,"%d",seconds);
   }


   sprintf(t,"%s:%s:%s:%s",dd, hh, mi, sec);
}

//-------------------------------------------------

                                 Thanks in advance, Robert ..!!
                                 robert.bralic@si.t-com.hr

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