68 lines
1.7 KiB
C
68 lines
1.7 KiB
C
/*
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* Copyright © 2009 Keith Packard <keithp@keithp.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (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 along
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* with this program; if not, write to the Free Software Foundation, Inc.,
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* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
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*/
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#include "aoview.h"
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static int16_t altitude_table[] = {
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#include "altitude.h"
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};
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#define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
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#define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
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int16_t
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aoview_pres_to_altitude(int16_t pres)
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{
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uint8_t o;
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int16_t part;
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if (pres < 0)
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pres = 0;
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o = pres >> ALT_FRAC_BITS;
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part = pres & ALT_FRAC_MASK;
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return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
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(int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
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}
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int16_t
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aoview_altitude_to_pres(int16_t alt)
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{
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int16_t span, sub_span;
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uint8_t l, h, m;
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int32_t pres;
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l = 0;
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h = NALT - 1;
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while ((h - l) != 1) {
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m = (l + h) >> 1;
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if (altitude_table[m] < alt)
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h = m;
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else
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l = m;
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}
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span = altitude_table[l] - altitude_table[h];
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sub_span = altitude_table[l] - alt;
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pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
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if (pres > 32767)
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pres = 32767;
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if (pres < 0)
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pres = 0;
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return (int16_t) pres;
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}
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