/*
 * $Header: /home/gene/library/website/docsrc/test-rpc/src/src/RCS/test0007.c,v 395.1 2008/04/20 17:25:55 gene Exp $
 *
 * Copyright (c) 2006 Gene Michael Stover.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or (at your option) any later version.
 *
 * This program 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 Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this program; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301
 * USA
 */
/*
 * Use a memory XDR stream to decode a bunch of double-precision
 * floating point numbers.
 * We hard-code the individual octets of the XDR stream, &
 * we check the values that it decodes.
 */

#include "this.h"

/*
 * Compare a decoded double value with an expected value.
 * Because we are dealing with floating point, we cannot
 * use a simple "=" comparison.  Instead, we check that
 * the numbers are close enough.
 * They are close enough if:
 *
 * 1. They have the same sign,
 * 
 * 2. They have the same magnitude (exponent), &
 *
 * 3. The different in the mantissas is at most the two
 * least significant bits.
 */
static bool_t
S_EqualDouble (double a, double b)
{
  static double mantissa = 52;          /* bits in the mantissa */
  static double forgiven_bits = 2;      /* bits of error we can ignore */
  double maximum_error;
  double error, relative_error;

  /*
   * The maximum error we're willing to accept is the "forgiven_bits"
   * most insignificant bits.  Here, we convert that to a scalar.
   */
  maximum_error = pow (2.0, forgiven_bits - mantissa);

  error = fabs (a - b);
#if 0
  printf ("\n%s:%d: error is %.3e.", __FILE__, __LINE__, error);
#endif
  if (error > 0.0) {
    relative_error = error / b;
  } else {
    /*
     * Absolute error is 0.0.  It has no representation as a
     * relative error.  So we'll treat it as a relative error
     * of zero.
     */
    relative_error = 0.0;
  }
#if 0
  printf ("\n%s:%d: relative error is %.3e.", __FILE__, __LINE__,
          relative_error);
#endif
  /*
   * A & B are equivalent if their error is less than the maximum
   * acceptable error, which was computed from a number of bits.
   */
  return relative_error < maximum_error;
}

int
main ()
{
  int rc = 0;
  static char pathname[] = "./src/test0007.data";
  FILE *fp;
  XDR xdr;
  static double a[] = { 0.0, -1.1e-1, M_PI, -2.2e2, 3.3e3, 4.4e-4,
                        -5.5e5, 6.6e-6 };
  static int alen = sizeof a / sizeof a[0];
  int i;
  double d;

  fp = fopen (pathname, "rb");
  if (fp != NULL) {
    xdrstdio_create (&xdr, fp, XDR_DECODE);
    for (i = 0; rc == 0 && i < alen; ++i) {
      if (xdr_double (&xdr, &d)) {
        if (S_EqualDouble (d, a[i])) {
          /* good so far */
        } else {
          printf ("\n%s:%d: xdr_double decoded %.18e.", __FILE__,
                  __LINE__, d);
          printf ("  Expected a[%d] = %.18e.", i, a[i]);
          rc = -47;
        }
      } else {
        printf ("\n%s:%d: xdr_double: %s", __FILE__, __LINE__,
                strerror (errno));
        rc = -46;
      }
    }
    xdr_destroy (&xdr);
    fclose (fp);
  } else {
    printf ("\n%s:%d: fopen: %s", __FILE__, __LINE__, strerror (errno));
    printf ("%s:%d: Could not open \"%s\" for binary input.", __FILE__,
            __LINE__, pathname);
    rc = 45;
  }
  return rc == 0 ? EXIT_SUCCESS : EXIT_FAILURE;
}

/* --- end of file --- */