src/main/common/gps_conversion.c

   1 /*
   2  * This file is part of Cleanflight.
   3  *
   4  * Cleanflight 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 3 of the License, or
   7  * (at your option) any later version.
   8  *
   9  * Cleanflight is distributed in the hope that it will be useful,
  10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12  * GNU General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with Cleanflight.  If not, see <http://www.gnu.org/licenses/>.
  16  */
  17
  18 #include <stdbool.h>
  19 #include <stdint.h>
  20 #include <ctype.h>
  21 #include <string.h>
  22
  23 #include "platform.h"
  24
  25 #include "common/string_light.h"
  26
  27 #ifdef USE_GPS
  28
  29
  30 #define DIGIT_TO_VAL(_x)    (_x - '0')
  31 uint32_t GPS_coord_to_degrees(const char* coordinateString)
  32 {
  33     const char *fieldSeparator, *remainingString;
  34     uint8_t degress = 0, minutes = 0;
  35     uint16_t fractionalMinutes = 0;
  36     uint8_t digitIndex;
  37
  38     // scan for decimal point or end of field
  39     for (fieldSeparator = coordinateString; sl_isdigit((unsigned char)*fieldSeparator); fieldSeparator++) {
  40         if (fieldSeparator >= coordinateString + 15)
  41             return 0; // stop potential fail
  42     }
  43     remainingString = coordinateString;
  44
  45     // convert degrees
  46     while ((fieldSeparator - remainingString) > 2) {
  47         if (degress)
  48             degress *= 10;
  49         degress += DIGIT_TO_VAL(*remainingString++);
  50     }
  51     // convert minutes
  52     while (fieldSeparator > remainingString) {
  53         if (minutes)
  54             minutes *= 10;
  55         minutes += DIGIT_TO_VAL(*remainingString++);
  56     }
  57     // convert fractional minutes
  58     // expect up to four digits, result is in
  59     // ten-thousandths of a minute
  60     if (*fieldSeparator == '.') {
  61         remainingString = fieldSeparator + 1;
  62         for (digitIndex = 0; digitIndex < 4; digitIndex++) {
  63             fractionalMinutes *= 10;
  64             if (sl_isdigit((unsigned char)*remainingString))
  65                 fractionalMinutes += *remainingString++ - '0';
  66         }
  67     }
  68     return degress * 10000000UL + (minutes * 1000000UL + fractionalMinutes * 100UL) / 6;
  69 }
  70 #endif