*
* 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; version 2 of the License.
+ * 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
#include "aoview.h"
-static int16_t altitude_table[2048] = {
+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)
{
- pres = pres >> 4;
- if (pres < 0) pres = 0;
- if (pres > 2047) pres = 2047;
- return altitude_table[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 pres;
+ int16_t span, sub_span;
+ uint8_t l, h, m;
+ int32_t pres;
- for (pres = 0; pres < 2047; pres++)
- if (altitude_table[pres] <= alt)
- break;
- return pres << 4;
+ 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;
}