src/marnav/ais/message.cpp

   1 #include "message.hpp"
   2 #include <algorithm>
   3
   4 namespace marnav
   5 {
   6 namespace ais
   7 {
   8 /// @cond DEV
   9 namespace
  10 {
  11 static const std::vector<std::pair<uint8_t, char>> SIXBIT_ASCII_TABLE = {
  12         {0, '@'}, {1, 'A'}, {2, 'B'}, {3, 'C'}, {4, 'D'}, {5, 'E'}, {6, 'F'}, {7, 'G'}, {8, 'H'},
  13         {9, 'I'}, {10, 'J'}, {11, 'K'}, {12, 'L'}, {13, 'M'}, {14, 'N'}, {15, 'O'}, {16, 'P'},
  14         {17, 'Q'}, {18, 'R'}, {19, 'S'}, {20, 'T'}, {21, 'U'}, {22, 'V'}, {23, 'W'}, {24, 'X'},
  15         {25, 'Y'}, {26, 'Z'}, {27, '['}, {28, '\\'}, {29, ']'}, {30, '^'}, {31, '_'}, {32, ' '},
  16         {33, '!'}, {34, '\"'}, {35, '#'}, {36, '$'}, {37, '%'}, {38, '&'}, {39, '\''}, {40, '('},
  17         {41, ')'}, {42, '*'}, {43, '+'}, {44, ','}, {45, '-'}, {46, '.'}, {47, '/'}, {48, '0'},
  18         {49, '1'}, {50, '2'}, {51, '3'}, {52, '4'}, {53, '5'}, {54, '6'}, {55, '7'}, {56, '8'},
  19         {57, '9'}, {58, ':'}, {59, ';'}, {60, '<'}, {61, '='}, {62, '>'}, {63, '?'},
  20 };
  21 }
  22 /// @endcond
  23
  24 char decode_sixbit_ascii(uint8_t value)
  25 {
  26         value &= 0x3f;
  27         auto i = std::find_if(SIXBIT_ASCII_TABLE.begin(), SIXBIT_ASCII_TABLE.end(),
  28                 [value](const std::pair<uint8_t, char> & p) { return p.first == value; });
  29         return i != SIXBIT_ASCII_TABLE.end() ? i->second : 0xff;
  30 }
  31
  32 uint8_t encode_sixbit_ascii(char c)
  33 {
  34         auto i = std::find_if(SIXBIT_ASCII_TABLE.begin(), SIXBIT_ASCII_TABLE.end(),
  35                 [c](const std::pair<uint8_t, char> & p) { return p.second == c; });
  36         return i != SIXBIT_ASCII_TABLE.end() ? i->first : 0xff;
  37 }
  38
  39 std::string trim_ais_string(const std::string & s) { return s.substr(0, s.find_first_of("@")); }
  40
  41 /// Reads a string from the AIS message at the specified offset.
  42 /// The string is decoded and returned.
  43 ///
  44 /// @param[in] bits The AIS message.
  45 /// @param[in] ofs The offset at which the string is being read.
  46 /// @param[in] count_sixbits Number of sixbits to be read.
  47 /// @return The decoded string.
  48 ///
  49 /// @todo consider to hide characters after '@'
  50 std::string message::read_string(
  51         const raw & bits, raw::size_type ofs, raw::size_type count_sixbits)
  52 {
  53         std::string s;
  54         s.reserve(count_sixbits);
  55
  56         for (raw::size_type i = 0; i < count_sixbits; ++i) {
  57                 uint8_t sixbit = 0;
  58                 bits.get(sixbit, ofs + i * 6, 6);
  59                 s += decode_sixbit_ascii(sixbit);
  60         }
  61
  62         return s;
  63 }
  64
  65 /// Writes the specified string into the AIS message. If the string does not fill
  66 /// the entire space within the message, fill characters `@` will be written
  67 /// until the specified number of sixbits is reached.
  68 ///
  69 /// @param[out] bits The AIS message.
  70 /// @param[in] ofs The offset at which the string is being written within the message.
  71 /// @param[in] count_sixbits Number of sixbits to write into the message.
  72 /// @param[in] s The string to be written.
  73 ///
  74 void message::write_string(
  75         raw & bits, raw::size_type ofs, raw::size_type count_sixbits, const std::string & s)
  76 {
  77         for (raw::size_type i = 0; i < count_sixbits; ++i) {
  78                 uint8_t value;
  79                 if (i < s.size()) {
  80                         value = encode_sixbit_ascii(s[i]);
  81                 } else {
  82                         value = encode_sixbit_ascii('@');
  83                 }
  84                 bits.set(value, ofs + i * 6, 6);
  85         }
  86 }
  87 }
  88 }