JB>   I removed your sqrt
   Good idea.
JB>   your 486sx25 should be as fast as your pentium was!
   Not quite... but better. :)
JB>   less efficient executables than turbo-c 2.0 :)
   QC2.5. It only does 286 optimizations, not 386.
JB>   upstep  -  I always wanted an excuse to use ^=
   Good idea, but I went with an array in steps of 30.
JB>   clock(), it starts at 0 when the prog begins
   I know, but I don't always have the timing loop as the
   whole program, so I habitually use variables. QC2.5 already
   gives program execution time at program exit. They match. :)
   Your code has a few flaws and I couldn't find command.com
   when I exited from running it in the IDE. I made a few more
   changes. You should get 3,513 primes less than 32768.
   This runs in about half a second when compiled under either
   QC2.5 ( 286 optimizations ) or BC++3.1 ( 386 optimizations )
   on a 486sx25 ( with show option disabled on the command line )
   and in about .05 seconds on a Pentium 166 system.
 /*_|_|   PRIMES.C
 _|_|_|   A program to find all signed integer primes.
 _|_|_|   No warrantee or guarantee is given or implied.
 _|_|_|   Released   PUBLIC DOMAIN   by Kurt Kuzba.  (8/6/98)*/
#include 
#include 
#include 
int main(int c, char **v)
{
   int ndx, check, prime, current, *primes, inc, root, show, ret;
   int incs[8] = { 2, 6, 4, 2, 4, 2, 4, 6 };
   float runtime = (float)clock();
   primes = malloc(32000 * sizeof(int));
   if(primes == NULL)
     return puts("Malloc failure");
   root = show = ret = 0;
   inc = 7;
   ndx = 9;
   primes[0] = 1, primes[1] = 2,  primes[2] = 3,  primes[3] = 5,
                  primes[4] = 7,  primes[5] = 11, primes[6] = 13,
                  primes[7] = 17, primes[8] = 19, primes[9] = 23;
   if(c > 1 && (v[1][0] == 's' || v[1][0] == 'S')) show++;
   for(current = 29; current > 0; current += incs[inc] )
   {
      inc = (inc + 1) % 8;
      check = prime = 1;
      while((long)current > ((long)root * (long)root))
         root++;
      while(prime && primes[++check] <= root)
         prime = current % primes[check];
      if(prime)
         if(show)
            printf("%7d%s",
               primes[++ndx] = current, !((++ret) % 10) ? "\n" :
"");
         else
            primes[++ndx] = current;
   }
   runtime = ((float)clock() - runtime) / CLK_TCK;
   printf("\n%d Primes found in %.2f seconds", ndx + 1, runtime);
   return 0;
}
 /*_|_|   end   PRIMES.C   */
                  or... if you dislike white space...
   /**/
   /**/
   /**/
   /**/
/**************/            /*********************/
#include           /**  Fire Torpedos!!  **/
#include           /*********************/
#include         /**/
int main(int c,char **v){int x,k,p,z,*r,i,o,w,e,n[8]={2,6,4,2,4,
2,4,6};float rt=(float)clock();r=malloc(32000*sizeof(int));if(NULL
==r)return puts("Malloc failure");o=w=e=0;i=7;x=9;r[0]=1,r[1]=2,r[2]
=3,r[3]=5,r[4]=7,r[5]=11,r[6]=13,r[7]=17,r[8]=19,r[9]=23;if(z>1&&(
v[1][0]=='s'||v[1][0]=='S'))w++;for(z=29;z>0;z+=n[i]){i=(i+1)%8;
k=p=1;while((long)z>((long)o*(long)o))o++;while(p&&r[++k]<=o)
p=z%r[k];if(p)if(w){printf("%7d%s",r[++x]=z,!((++e)%10)?"\n":
"");}else r[++x]=z;}rt=((float)clock()-rt)/CLK_TCK;printf(    /*(====)*/
"\n%d Primes found in %.2f seconds",x+1,rt);return 0;}

> ] Some people dream in Black & White. I just dream in black...

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