pi.c

/*
  This program computes the value of "pi".
  
  Run time ./pi

  Output should be something like:

Pi is 3.141593                        <-- (output from pi.c)
29.7u 0.0s 0:29 99% 0+0k 0+0io 0pf+0w <-- (output from time command)
  ^    ^    ^
  |    |    (elapsed real runtime used by our program)
  |    (CPU-seconds used by system on behalf of user program)
  (CPU-seconds used directly by user program)
*/

/* This is the original serial code */

#include <stdio.h>

const long num_intervals = 1000000000;

double f( double a )
{
  return (4.0 / (1.0 + a*a));
}

main()
{
  double h, sum, x, pi;
  long i;

  h   = 1.0 / (double)num_intervals;
  sum = 0.0;

  for (i = 0; i < num_intervals; i++) {
    x = h * ((double)i + 0.5);
    sum += f(x);
  }

  pi = h * sum;

  printf( "Pi is %f\n", pi );
}