src/NMEA/Checksum.hpp

   1 /*
   2 Copyright_License {
   3
   4   XCSoar Glide Computer - http://www.xcsoar.org/
   5   Copyright (C) 2000-2013 The XCSoar Project
   6   A detailed list of copyright holders can be found in the file "AUTHORS".
   7
   8   This program is free software; you can redistribute it and/or
   9   modify it under the terms of the GNU General Public License
  10   as published by the Free Software Foundation; either version 2
  11   of the License, or (at your option) any later version.
  12
  13   This program is distributed in the hope that it will be useful,
  14   but WITHOUT ANY WARRANTY; without even the implied warranty of
  15   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16   GNU General Public License for more details.
  17
  18   You should have received a copy of the GNU General Public License
  19   along with this program; if not, write to the Free Software
  20   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  21 }
  22 */
  23
  24 #ifndef XCSOAR_NMEA_CHECKSUM_HPP
  25 #define XCSOAR_NMEA_CHECKSUM_HPP
  26
  27 #include "Compiler.h"
  28
  29 #include <stdint.h>
  30
  31 /**
  32  * Calculates the checksum for the specified line (without the
  33  * asterisk and the newline character).
  34  *
  35  * @param p a NULL terminated string
  36  */
  37 gcc_pure
  38 static inline uint8_t
  39 NMEAChecksum(const char *p)
  40 {
  41   uint8_t checksum = 0;
  42
  43   /* skip the dollar sign at the beginning (the exclamation mark is
  44      used by CAI302 */
  45   if (*p == '$' || *p == '!')
  46     ++p;
  47
  48   while (*p != 0)
  49     checksum ^= *p++;
  50
  51   return checksum;
  52 }
  53
  54 /**
  55  * Calculates the checksum for the specified line (without the
  56  * asterisk and the newline character).
  57  *
  58  * @param p a string
  59  * @param length the number of characters in the string
  60  */
  61 gcc_pure
  62 static inline uint8_t
  63 NMEAChecksum(const char *p, unsigned length)
  64 {
  65   uint8_t checksum = 0;
  66
  67   unsigned i = 0;
  68
  69   /* skip the dollar sign at the beginning (the exclamation mark is
  70      used by CAI302 */
  71   if (length > 0 && (*p == '$' || *p == '!')) {
  72     ++i;
  73     ++p;
  74   }
  75
  76   for (; i < length; ++i)
  77     checksum ^= *p++;
  78
  79   return checksum;
  80 }
  81
  82 /**
  83  * Verify the NMEA checksum at the end of the specified string,
  84  * separated with an asterisk ('*').
  85  */
  86 gcc_pure
  87 bool
  88 VerifyNMEAChecksum(const char *p);
  89
  90 /**
  91  * Caclulates the checksum of the specified string, and appends it at
  92  * the end, preceded by an asterisk ('*').
  93  */
  94 void
  95 AppendNMEAChecksum(char *p);
  96
  97 #endif