Museum

     Name
          difftime - Computes the difference between time values.

     Syntax
          #include <time.h>

          double difftime(time2, time1)
          time_t time2;
          time_t time1;

     Description
          The difftime function computes the difference of time2 -
          time1.

     Return Value
          The difftime function returns the elapsed time in seconds
          from time1 to time2 as a double-precision number.

     See Also
          time(S)

     Example
          #include <time.h>

          int mark[10000];

          main() {
                  time_t  start, finish;
                  register int i, loop, n, num, step;
                  time(&start);
                  for (loop = 0; loop < 1000; ++loop)
                     for (num = 0,n = 3; n < 10000; n += 2)
                          if (!mark[n])
                             {
                             step = 2*n;
                             for (i = 3*n; i < 10000; i += step)
                               mark[i] = -1;
                             ++num;
                             }
                  time(&finish);

                  /* Prints average of 1000 loops through "sieve": */
                  printf("\nProgram takes %f seconds to find %d
          primes.\n",           difftime(finish, start)/1000, num); }

          Output:

          Program takes 0.482000 seconds to find 1228 primes.

          This program calculates the amount of time needed to find
          the prime numbers between 3 and 10,000.

                                                (printed 6/18/89)