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/* interpolation/integ_eval_macro.h
*
* Copyright (C) 1996, 1997, 1998, 1999, 2000 Gerard Jungman
*
* 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; 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
* 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
*/
/* function for doing the spline integral evaluation
which is common to both the cspline and akima methods
*/
static inline double
integ_eval (double ai, double bi, double ci, double di, double xi, double a,
double b)
{
const double r1 = a - xi;
const double r2 = b - xi;
const double r12 = r1 + r2;
const double bterm = 0.5 * bi * r12;
const double cterm = (1.0 / 3.0) * ci * (r1 * r1 + r2 * r2 + r1 * r2);
const double dterm = 0.25 * di * r12 * (r1 * r1 + r2 * r2);
return (b - a) * (ai + bterm + cterm + dterm);
}
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