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183 lines
5.2 KiB
C++
183 lines
5.2 KiB
C++
// Copyright 2020 Mobilinkd LLC.
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#pragma once
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#include <array>
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#include <cstdint>
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#include <cmath>
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#include <stdexcept>
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#include <algorithm>
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#include "export.h"
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namespace modemm17
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{
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struct MODEMM17_API LinkSetupFrame
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{
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using call_t = std::array<char,10>; // NUL-terminated C-string.
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using encoded_call_t = std::array<uint8_t, 6>;
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using gnss_t = std::array<uint8_t, 14>;
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using frame_t = std::array<uint8_t, 30>;
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static const encoded_call_t BROADCAST_ADDRESS;
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static const call_t BROADCAST_CALL;
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enum TxType { PACKET, STREAM };
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enum DataType { DT_RESERVED, DATA, VOICE, MIXED };
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enum EncType { NONE, AES, LFSR, ET_RESERVED };
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call_t tocall_ = {0}; // Destination
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call_t mycall_ = {0}; // Source
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TxType tx_type_ = TxType::STREAM;
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DataType data_type_ = DataType::VOICE;
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EncType encryption_type_ = EncType::NONE;
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/**
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* The callsign is encoded in base-40 starting with the right-most
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* character. The final value is written out in "big-endian" form, with
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* the most-significant value first. This leads to 0-padding of shorter
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* callsigns.
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*
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* @param[in] callsign is the callsign to encode.
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* @param[in] strict is a flag (disabled by default) which indicates whether
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* invalid characters are allowed and assugned a value of 0 or not allowed,
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* resulting in an exception.
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* @return the encoded callsign as an array of 6 bytes.
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* @throw invalid_argument when strict is true and an invalid callsign (one
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* containing an unmappable character) is passed.
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*/
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static encoded_call_t encode_callsign(call_t callsign, bool strict = false)
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{
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// Encode the characters to base-40 digits.
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uint64_t encoded = 0;
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std::reverse(callsign.begin(), callsign.end());
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for (auto c : callsign)
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{
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encoded *= 40;
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if ((c >= 'A') && (c <= 'Z'))
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{
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encoded += c - 'A' + 1;
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}
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else if ((c >= '0') && (c <= '9'))
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{
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encoded += c - '0' + 27;
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}
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else if (c == '-')
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{
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encoded += 37;
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}
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else if (c == '/')
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{
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encoded += 38;
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}
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else if (c == '.')
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{
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encoded += 39;
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}
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else if (strict)
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{
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throw std::invalid_argument("bad callsign");
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}
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}
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const auto p = reinterpret_cast<uint8_t*>(&encoded);
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encoded_call_t result;
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std::copy(p, p + 6, result.rbegin());
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return result;
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}
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/**
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* Decode a base-40 encoded callsign to its text representation. This decodes
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* a 6-byte big-endian value into a string of up to 9 characters.
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*/
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static call_t decode_callsign(encoded_call_t callsign)
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{
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static const char callsign_map[] = "xABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-/.";
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call_t result;
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if (callsign == BROADCAST_ADDRESS)
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{
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result = BROADCAST_CALL;
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return result;
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}
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uint64_t encoded = 0; // This only works on little endian architectures.
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auto p = reinterpret_cast<uint8_t*>(&encoded);
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std::copy(callsign.rbegin(), callsign.rend(), p);
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// decode each base-40 digit and map them to the appriate character.
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result.fill(0);
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size_t index = 0;
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while (encoded)
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{
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result[index++] = callsign_map[encoded % 40];
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encoded /= 40;
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}
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return result;
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}
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static gnss_t encode_gnss(float lat, float lon, float alt)
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{
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gnss_t result;
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result.fill(0);
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double lat_int, lat_frac;
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double lon_int, lon_frac;
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uint16_t lat_dec, lon_dec;
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lat_frac = modf(lat, &lat_int);
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lon_frac = modf(lon, &lon_int);
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bool north = lat_int >= 0;
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bool east = lon_int >= 0;
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result[2] = (int) std::abs(lat_int);
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lat_dec = std::abs(lat_frac) * 65536.0f;
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result[3] = lat_dec >> 8;
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result[4] = lat_dec & 0xFF;
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result[5] = (int) std::abs(lon_int);
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lon_dec = std::abs(lon_frac) * 65536.0f;
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result[6] = lon_dec >> 8;
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result[7] = lon_dec & 0xFF;
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result[8] = (north ? 0 : 1) | ((east ? 0 : 1)<<1) | (1<<2);
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uint16_t alt_enc = (alt * 3.28084f) + 1500;
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result[9] = alt_enc >> 8;
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result[10] = alt_enc & 0xFF;
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return result;
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}
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static void decode_gnss(const gnss_t& gnss_enc, float& lat, float& lon, float& alt)
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{
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bool north = (gnss_enc[8] & 1) != 0;
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bool east = (gnss_enc[8] & 2) != 0;
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uint32_t lat_int = gnss_enc[2];
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uint16_t lat_frac = (gnss_enc[3] << 8) + gnss_enc[4];
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uint32_t lon_int = gnss_enc[5];
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uint16_t lon_frac = (gnss_enc[6] << 8) + gnss_enc[7];
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lat = lat_int + (lat_frac / 65536.0f);
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lat = north ? lat : -lat;
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lon = lon_int + (lon_frac / 65536.0f);
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lat = east ? lon : -lon;
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uint16_t alt_enc = (gnss_enc[9] << 8) + gnss_enc[10];
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alt = (alt_enc - 1500) / 3.28084f;
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}
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LinkSetupFrame()
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{}
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LinkSetupFrame& myCall(const char*)
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{
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return *this;
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}
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};
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} // modemm17
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