2 * Copyright © 2009 Keith Packard <keithp@keithp.com>
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful, but
10 * WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 * General Public License for more details.
14 * You should have received a copy of the GNU General Public License along
15 * with this program; if not, write to the Free Software Foundation, Inc.,
16 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
21 static int16_t altitude_table[] = {
25 #define ALT_FRAC_SCALE (1 << ALT_FRAC_BITS)
26 #define ALT_FRAC_MASK (ALT_FRAC_SCALE - 1)
29 aoview_pres_to_altitude(int16_t pres)
36 o = pres >> ALT_FRAC_BITS;
37 part = pres & ALT_FRAC_MASK;
39 return ((int32_t) altitude_table[o] * (ALT_FRAC_SCALE - part) +
40 (int32_t) altitude_table[o+1] * part + (ALT_FRAC_SCALE >> 1)) >> ALT_FRAC_BITS;
44 aoview_altitude_to_pres(int16_t alt)
46 int16_t span, sub_span;
52 while ((h - l) != 1) {
54 if (altitude_table[m] < alt)
59 span = altitude_table[l] - altitude_table[h];
60 sub_span = altitude_table[l] - alt;
61 pres = ((((int32_t) l * (span - sub_span) + (int32_t) h * sub_span) << ALT_FRAC_BITS) + (span >> 1)) / span;
66 return (int16_t) pres;