/*

 * Copyright 2011 Steven Gribble

 *

 *  This file is the solution to an exercise problem posed during

 *  one of the UW CSE 333 lectures (333exercises).

 *

 *  333exercises is free software: you can redistribute it and/or modify

 *  it under the terms of the GNU General Public License as published by

 *  the Free Software Foundation, either version 3 of the License, or

 *  (at your option) any later version.

 *

 *  333exercises is distributed in the hope that it will be useful,

 *  but WITHOUT ANY WARRANTY; without even the implied warranty of

 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 *  GNU General Public License for more details.

 *

 *  You should have received a copy of the GNU General Public License

 *  along with 333exercises.  If not, see <http://www.gnu.org/licenses/>.

 */



#include <stdio.h>

#include <stdlib.h>

#include <assert.h>

#include <signal.h>

#include <math.h>



#include "complex.h"



// We use the following global variable to check whether

// a divide-by-zero exception is expected or not.  We'll

// start out not expecting it, and we'll set this to 1 when

// we test a complex division that should trigger a divide by

// zero exception.

static int expect_divzero = 0;



// This is a "signal handler"; in main(), we register this function

// with the operating system using the "sigaction()" system call.

// Do a "man sigaction" to learn about it.

static void handle_divzero(int sig, siginfo_t *si, void *data) {

  assert(expect_divzero == 1);

  exit(0);  // terminate the process; same as "return 0;" from main

}





// Because floating points are an approximate rather than exact

// representation, you can't directly compare two C doubles and

// expect it to work.  Instead, you need to compare for equality

// within some threshold.  This helper function DoubleEqualsEpsilon

// and EPSILON #define do this.

#define EPSILON ((double) 0.000000000001)

static int DoubleEqualsEpsilon(double a, double b) {

  if (a > b) {

    // a > b case

    if ((a - b) < EPSILON)

      return 1;

    return 0;

  }



  // b <= a case

  if ((b - a) < EPSILON)

    return 1;

  return 0;

}



int main(int argc, char **argv) {

  Complex a = {1, 2}, b = {3, 4}, c = {0, 0};

  Complex res;

  struct sigaction act, oldact;



  // register our SIGFPE floating point handler

  act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;

  act.sa_sigaction = &handle_divzero;

  assert(sigaction(SIGFPE, &act, &oldact) == 0);



  res = ComplexAdd(a, b);

  assert(DoubleEqualsEpsilon(res.real, 4.0) == 1);

  assert(DoubleEqualsEpsilon(res.imaginary, 6.0) == 1);



  res = ComplexSubtract(a, b);

  assert(DoubleEqualsEpsilon(res.real, -2.0) == 1);

  assert(DoubleEqualsEpsilon(res.imaginary, -2.0) == 1);



  res = ComplexMultiply(a, b);

  assert(DoubleEqualsEpsilon(res.real, -5) == 1);

  assert(DoubleEqualsEpsilon(res.imaginary, 2.0) == 1);



  res = ComplexDivide(a, b);

  assert(DoubleEqualsEpsilon(res.real, 0.44) == 1);

  assert(DoubleEqualsEpsilon(res.imaginary, 0.08) == 1);



  // Test the "divide by zero" case.  On modern Intel

  // machines and Linux, this causes the returned

  // Complex to contain the value "NAN" in both the

  // real and imaginary components.  The <math.h>

  // function "isnan()" is how we compare to NAN.

  // But, to be super paranoid, we've also set up

  // a signal handler to catch a SIGFPE floating point

  // exception (which integer divide by zero throws).

  expect_divzero = 1;

  res = ComplexDivide(a, c);

  assert(isnan(res.real));

  assert(isnan(res.imaginary));



  return EXIT_SUCCESS;

}