--- /dev/null
+/*
+ * 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; version 2 of the License.
+ *
+ * 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.
+ */
+
+#if !defined(AO_CONVERT_TEST) && !defined(AO_FLIGHT_TEST)
+#include "ao.h"
+#endif
+
+static const 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
+ao_pres_to_altitude(int16_t pres) __reentrant
+{
+ 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;
+}
+
+#if AO_NEED_ALTITUDE_TO_PRES
+int16_t
+ao_altitude_to_pres(int16_t alt) __reentrant
+{
+ 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;
+}
+#endif
+
+#if 0
+int16_t
+ao_temp_to_dC(int16_t temp) __reentrant
+{
+ int16_t ret;
+
+ /* Output voltage at 0°C = 0.755V
+ * Coefficient = 0.00247V/°C
+ * Reference voltage = 1.25V
+ *
+ * temp = ((value / 32767) * 1.25 - 0.755) / 0.00247
+ * = (value - 19791.268) / 32768 * 1.25 / 0.00247
+ * ≃ (value - 19791) * 1012 / 65536
+ */
+ ret = ((temp - 19791) * 1012L) >> 16;
+ return ret;
+}
+#endif