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interpolate.c

/*
 *  acm : an aerial combat simulator for X
 *  Copyright (C) 1991,1992  Riley Rainey
 *
 *  This program 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; version 2 dated June, 1991.
 *
 *  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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program;  if not, write to the Free Software
 *  Foundation, Inc., 675 Mass Ave., Cambridge, MA 02139, USA.
 */

#include "interpolate.h"
#include <stdio.h>
#ifdef DUMP
#include <signal.h>
#endif

/*
 *  interpolate :  determine the value of a function of one variable
 *             by interpolation.  Interpolation tables are built by
 *             the ibuild utility.
 */

static char *ierrmsg = "interpolate: x value is out of bounds\n";

float_t
interpolate (table, x)
ITable      *table;
double      x;
{

      register int i, count = table->count;

      if (x < table->minX) {
            fprintf (stderr, ierrmsg);
            fprintf (stderr, "minimum x = %g; x = %g\n", table->minX, x);
#ifdef DUMP
            kill (getpid(), SIGBUS);
#endif
            return (float_t) I_NaN;
      }

      for (i=0; i<count; ++i) {
          if (x <= table->entry[i].x)
            return (float_t)(table->entry[i].m * x + table->entry[i].b);
      }

      fprintf (stderr, ierrmsg);
      fprintf (stderr, "maximum x = %g; x = %g\n", table->entry[i-1].x, x);

#ifdef DUMP
      kill (getpid(), SIGBUS);
#endif

      return (float_t) I_NaN;
}

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