mirror of
https://github.com/eried/portapack-mayhem.git
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0789d50fdf
Templatize PacketBuilder to optionally bit unstuff, and have flexible packet termination behavior.
377 lines
9.8 KiB
C++
377 lines
9.8 KiB
C++
/*
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* Copyright (C) 2015 Jared Boone, ShareBrained Technology, Inc.
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*
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* This file is part of PortaPack.
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, Inc., 51 Franklin Street,
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* Boston, MA 02110-1301, USA.
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*/
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#include "ais_baseband.hpp"
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#include <cstdint>
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#include <cstddef>
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#include <cstdlib>
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#include <string>
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#include "crc.hpp"
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// TODO: Move string formatting elsewhere!!!
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#include "ui_widget.hpp"
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namespace baseband {
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template<typename T, typename BitRemap>
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class FieldReader {
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public:
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constexpr FieldReader(
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const T& data
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) : data { data }
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{
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}
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uint32_t read(const size_t start_bit, const size_t length) const {
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uint32_t value = 0;
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for(size_t i=start_bit; i<(start_bit + length); i++) {
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value = (value << 1) | data[bit_remap(i)];
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}
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return value;
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}
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private:
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const T& data;
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const BitRemap bit_remap { };
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};
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namespace ais {
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struct BitRemap {
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size_t operator()(const size_t bit_index) const {
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return bit_index ^ 7;
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}
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};
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struct CRCBitRemap {
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size_t operator()(const size_t bit_index) const {
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return bit_index;
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}
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};
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using FieldReader = baseband::FieldReader<std::bitset<1024>, BitRemap>;
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using CRCFieldReader = baseband::FieldReader<std::bitset<1024>, CRCBitRemap>;
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struct PacketLengthRange {
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constexpr PacketLengthRange(
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) : min_bytes { 0 },
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max_bytes { 0 }
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{
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}
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constexpr PacketLengthRange(
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const uint16_t min_bits,
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const uint16_t max_bits
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) : min_bytes { static_cast<uint8_t>(min_bits / 8U) },
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max_bytes { static_cast<uint8_t>(max_bits / 8U) }
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{
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// static_assert((min_bits & 7) == 0, "minimum bits not a multiple of 8");
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// static_assert((max_bits & 7) == 0, "minimum bits not a multiple of 8");
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}
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bool contains(const size_t bit_count) const {
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return !is_above(bit_count) && !is_below(bit_count);
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}
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bool is_above(const size_t bit_count) const {
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return (min() > bit_count);
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}
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bool is_below(const size_t bit_count) const {
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return (max() < bit_count);
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}
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size_t min() const {
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return min_bytes * 8;
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}
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size_t max() const {
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return max_bytes * 8;
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}
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private:
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const uint8_t min_bytes;
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const uint8_t max_bytes;
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};
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static constexpr std::array<PacketLengthRange, 64> packet_length_range { {
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{ 0, 0 }, // 0
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{ 168, 168 }, // 1
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{ 168, 168 }, // 2
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{ 168, 168 }, // 3
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{ 168, 168 }, // 4
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{ 424, 424 }, // 5
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{ 0, 0 }, // 6
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{ 0, 0 }, // 7
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{ 0, 1008 }, // 8
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{ 0, 0 }, // 9
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{ 0, 0 }, // 10
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{ 0, 0 }, // 11
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{ 0, 0 }, // 12
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{ 0, 0 }, // 13
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{ 0, 0 }, // 14
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{ 0, 0 }, // 15
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{ 0, 0 }, // 16
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{ 0, 0 }, // 17
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{ 168, 168 }, // 18
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{ 0, 0 }, // 19
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{ 72, 160 }, // 20
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{ 272, 360 }, // 21
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{ 168, 168 }, // 22
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{ 160, 160 }, // 23
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{ 160, 168 }, // 24
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{ 0, 168 }, // 25
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{ 0, 0 }, // 26
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{ 0, 0 }, // 27
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{ 0, 0 }, // 28
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{ 0, 0 }, // 29
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{ 0, 0 }, // 30
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{ 0, 0 }, // 31
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} };
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struct PacketLengthValidator {
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bool operator()(const uint_fast8_t message_id, const size_t length) {
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return packet_length_range[message_id].contains(length);
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}
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};
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struct PacketTooLong {
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bool operator()(const uint_fast8_t message_id, const size_t length) {
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return packet_length_range[message_id].is_below(length);
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}
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};
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struct CRCCheck {
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bool operator()(const std::bitset<1024>& payload, const size_t data_length) {
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CRCFieldReader field_crc { payload };
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CRC<uint16_t> ais_fcs { 0x1021 };
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uint16_t crc_calculated = 0xffff;
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for(size_t i=0; i<data_length + 16; i+=8) {
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if( i == data_length ) {
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crc_calculated ^= 0xffff;
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}
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const uint8_t byte = field_crc.read(i, 8);
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crc_calculated = ais_fcs.calculate_byte(crc_calculated, byte);
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}
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return crc_calculated == 0x0000;
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}
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};
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static int32_t ais_latitude_normalized(
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const FieldReader& field,
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const size_t start_bit
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) {
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// Shifting and dividing is to sign-extend the source field.
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// TODO: There's probably a more elegant way to do it.
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return static_cast<int32_t>(field.read(start_bit, 27) << 5) / 32;
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}
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static int32_t ais_longitude_normalized(
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const FieldReader& field,
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const size_t start_bit
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) {
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// Shifting and dividing is to sign-extend the source field.
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// TODO: There's probably a more elegant way to do it.
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return static_cast<int32_t>(field.read(start_bit, 28) << 4) / 16;
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}
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static std::string ais_format_latlon_normalized(const int32_t normalized) {
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const int32_t t = (normalized * 5) / 3;
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const int32_t degrees = t / (100 * 10000);
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const int32_t fraction = std::abs(t) % (100 * 10000);
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return ui::to_string_dec_int(degrees) + "." + ui::to_string_dec_int(fraction, 6, '0');
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}
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static std::string ais_format_latitude(
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const FieldReader& field,
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const size_t start_bit
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) {
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const auto value = static_cast<int32_t>(field.read(start_bit, 27) << 5) / 32;
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return ais_format_latlon_normalized(value);
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}
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static std::string ais_format_longitude(
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const FieldReader& field,
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const size_t start_bit
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) {
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const auto value = static_cast<int32_t>(field.read(start_bit, 28) << 4) / 16;
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return ais_format_latlon_normalized(value);
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}
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struct ais_datetime {
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uint16_t year;
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uint8_t month;
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uint8_t day;
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uint8_t hour;
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uint8_t minute;
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uint8_t second;
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};
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static ais_datetime ais_get_datetime(
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const FieldReader& field,
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const size_t start_bit
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) {
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return {
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static_cast<uint16_t>(field.read(start_bit + 0, 14)),
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static_cast<uint8_t >(field.read(start_bit + 14, 4)),
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static_cast<uint8_t >(field.read(start_bit + 18, 5)),
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static_cast<uint8_t >(field.read(start_bit + 23, 5)),
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static_cast<uint8_t >(field.read(start_bit + 28, 6)),
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static_cast<uint8_t >(field.read(start_bit + 34, 6)),
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};
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}
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static std::string ais_format_datetime(
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const FieldReader& field,
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const size_t start_bit
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) {
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const auto datetime = ais_get_datetime(field, start_bit);
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return ui::to_string_dec_uint(datetime.year, 4) + "/" +
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ui::to_string_dec_uint(datetime.month, 2, '0') + "/" +
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ui::to_string_dec_uint(datetime.day, 2, '0') + " " +
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ui::to_string_dec_uint(datetime.hour, 2, '0') + ":" +
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ui::to_string_dec_uint(datetime.minute, 2, '0') + ":" +
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ui::to_string_dec_uint(datetime.second, 2, '0');
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}
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static char ais_char_to_ascii(const uint8_t c) {
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return (c ^ 32) + 32;
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}
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static std::string ais_read_text(
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const FieldReader& field,
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const size_t start_bit,
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const size_t character_count
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) {
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std::string result;
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const size_t character_length = 6;
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const size_t end_bit = start_bit + character_count * character_length;
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for(size_t i=start_bit; i<end_bit; i+=character_length) {
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result += ais_char_to_ascii(field.read(i, character_length));
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}
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return result;
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}
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static std::string ais_format_navigational_status(const unsigned int value) {
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switch(value) {
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case 0: return "under way w/engine";
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case 1: return "at anchor";
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case 2: return "not under command";
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case 3: return "restricted maneuv";
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case 4: return "constrained draught";
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case 5: return "moored";
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case 6: return "aground";
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case 7: return "fishing";
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case 8: return "sailing";
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case 9: case 10: case 13: return "reserved";
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case 11: return "towing astern";
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case 12: return "towing ahead/along";
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case 14: return "SART/MOB/EPIRB";
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case 15: return "undefined";
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default: return "unexpected";
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}
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}
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decoded_packet packet_decode(const std::bitset<1024>& payload, const size_t payload_length) {
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// TODO: Unstuff here, not in baseband!
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// Subtract end flag (6 bits) + one unstuffing bit (occurs during end flag).
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const size_t data_and_fcs_length = payload_length - 7;
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if( data_and_fcs_length < 38 ) {
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return { "short " + ui::to_string_dec_uint(data_and_fcs_length, 3), "" };
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}
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const size_t extra_bits = data_and_fcs_length & 7;
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if( extra_bits != 0 ) {
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return { "extra bits " + ui::to_string_dec_uint(data_and_fcs_length, 3), "" };
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}
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FieldReader field { payload };
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const auto message_id = field.read(0, 6);
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const size_t data_length = data_and_fcs_length - 16;
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PacketLengthValidator packet_length_valid;
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if( !packet_length_valid(message_id, data_length) ) {
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return { "bad length " + ui::to_string_dec_uint(data_length, 3), "" };
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}
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CRCCheck crc_ok;
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if( !crc_ok(payload, data_length) ) {
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return { "crc", "" };
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}
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const auto source_id = field.read(8, 30);
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std::string result { ui::to_string_dec_uint(message_id, 2) + " " + ui::to_string_dec_uint(source_id, 10) };
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switch(message_id) {
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case 1:
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case 2:
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case 3:
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{
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const auto navigational_status = field.read(38, 4);
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result += " " + ais_format_navigational_status(navigational_status);
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result += " " + ais_format_latlon_normalized(ais_latitude_normalized(field, 89));
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result += " " + ais_format_latlon_normalized(ais_longitude_normalized(field, 61));
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}
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break;
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case 4:
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{
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result += " " + ais_format_datetime(field, 38);
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result += " " + ais_format_latlon_normalized(ais_latitude_normalized(field, 107));
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result += " " + ais_format_latlon_normalized(ais_longitude_normalized(field, 79));
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}
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break;
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case 5:
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{
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const auto call_sign = ais_read_text(field, 70, 7);
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const auto name = ais_read_text(field, 112, 20);
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const auto destination = ais_read_text(field, 302, 20);
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result += " \"" + call_sign + "\" \"" + name + "\" \"" + destination + "\"";
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}
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break;
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case 21:
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{
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const auto name = ais_read_text(field, 43, 20);
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result += " \"" + name + "\" " + ais_format_latitude(field, 192) + " " + ais_format_longitude(field, 164);
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}
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break;
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default:
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break;
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}
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return { "OK", result };
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}
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} /* namespace ais */
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} /* namespace baseband */
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