kopia lustrzana https://github.com/f4exb/sdrangel
132 wiersze
3.7 KiB
C++
132 wiersze
3.7 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 <string_view> // Don't have std::span in C++17.
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#include <stdexcept>
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#include <algorithm>
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namespace mobilinkd
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{
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struct 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 frame_t = std::array<uint8_t, 30>;
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static constexpr encoded_call_t BROADCAST_ADDRESS = {0xff, 0xff, 0xff, 0xff, 0xff, 0xff};
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static constexpr call_t BROADCAST_CALL = {'B', 'R', 'O', 'A', 'D', 'C', 'A', 'S', 'T', 0};
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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' and 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' and 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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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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} // mobilinkd
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