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/*
* Copyright © 2009 Keith Packard <keithp@keithp.com>
*
* 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.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
*/
#include "aoview.h"
static int16_t altitude_table[] = {
#include "altitude.h"
};
#define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
#define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
int16_t
aoview_pres_to_altitude(int16_t pres)
{
uint8_t o;
int16_t part;
if (pres < 0)
pres = 0;
o = pres >> ALT_FRAC_BITS;
part = pres & ALT_FRAC_MASK;
return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
(int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
}
int16_t
aoview_altitude_to_pres(int16_t alt)
{
int16_t span, sub_span;
uint8_t l, h, m;
int32_t pres;
l = 0;
h = NALT - 1;
while ((h - l) != 1) {
m = (l + h) >> 1;
if (altitude_table[m] < alt)
h = m;
else
l = m;
}
span = altitude_table[l] - altitude_table[h];
sub_span = altitude_table[l] - alt;
pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
if (pres > 32767)
pres = 32767;
if (pres < 0)
pres = 0;
return (int16_t) pres;
}
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