108 lines
2.6 KiB
C++
108 lines
2.6 KiB
C++
//
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// interpolater.cxx -- routines to handle linear interpolation from a table of
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// x,y The table must be sorted by "x" in ascending order
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//
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// Written by Curtis Olson, started April 1998.
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//
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// Copyright (C) 1998 Curtis L. Olson - curt@me.umn.edu
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//
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// This program is free software; you can redistribute it and/or
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// modify it under the terms of the GNU General Public License as
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// published by the Free Software Foundation; either version 2 of the
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// License, or (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful, but
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// WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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// General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program; if not, write to the Free Software
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// Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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//
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// $Id$
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#include <Include/compiler.h>
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#ifdef __MWERKS__
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#include <stdlib.h> // for exit()
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#endif
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#include STL_STRING
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#include <Debug/logstream.hxx>
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#include <Include/fg_zlib.h>
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#include <Misc/fgstream.hxx>
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#include "interpolater.hxx"
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// Constructor -- loads the interpolation table from the specified
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// file
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fgINTERPTABLE::fgINTERPTABLE( const string& file ) {
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FG_LOG( FG_MATH, FG_INFO, "Initializing Interpolator for " << file );
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fg_gzifstream in( file );
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if ( !in ) {
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FG_LOG( FG_GENERAL, FG_ALERT, "Cannot open file: " << file );
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exit(-1);
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}
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size = 0;
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in >> skipcomment;
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while ( in ) {
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if ( size < MAX_TABLE_SIZE ) {
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in >> table[size][0] >> table[size][1];
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size++;
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} else {
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FG_LOG( FG_MATH, FG_ALERT,
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"fgInterpolateInit(): Exceed max table size = "
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<< MAX_TABLE_SIZE );
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exit(-1);
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}
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}
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}
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// Given an x value, linearly interpolate the y value from the table
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double fgINTERPTABLE::interpolate(double x) {
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int i;
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double y;
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i = 0;
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while ( (x > table[i][0]) && (i < size) ) {
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i++;
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}
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// printf ("i = %d ", i);
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if ( (i == 0) && (x < table[0][0]) ) {
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FG_LOG( FG_MATH, FG_ALERT,
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"fgInterpolateInit(): lookup error, x to small = " << x );
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return(0.0);
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}
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if ( x > table[i][0] ) {
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FG_LOG( FG_MATH, FG_ALERT,
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"fgInterpolateInit(): lookup error, x to big = " << x );
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return(0.0);
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}
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// y = y1 + (y0 - y1)(x - x1) / (x0 - x1)
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y = table[i][1] +
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( (table[i-1][1] - table[i][1]) *
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(x - table[i][0]) ) /
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(table[i-1][0] - table[i][0]);
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return(y);
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}
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// Destructor
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fgINTERPTABLE::~fgINTERPTABLE( void ) {
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}
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