+ 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;