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Code Issues Releases Wiki Activity

Improve CRC computation of ISM

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This commit is contained in:
Carles Fernandez
2024-09-20 18:54:18 +02:00
parent db78d104bf
commit de6f991811
4 changed files with 28 additions and 28 deletions
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29
src/core/system_parameters/galileo_ism.cc
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@@ -15,9 +15,7 @@
*/
#include "galileo_ism.h"
#include <boost/dynamic_bitset.hpp>
#include <algorithm>
#include <vector>
void Galileo_ISM::set_ism_constellation_id(uint8_t const_id)
{
@@ -177,12 +175,27 @@ uint16_t Galileo_ISM::get_Tvalidity_hours() const
bool Galileo_ISM::check_ism_crc(const std::bitset<GALILEO_DATA_JK_BITS>& bits)
{
boost::dynamic_bitset<unsigned char> frame_bits(bits.to_string().substr(0, GALILEO_ISM_CRC_DATA_BITS));
std::vector<unsigned char> bytes;
boost::to_block_range(frame_bits, std::back_inserter(bytes));
std::reverse(bytes.begin(), bytes.end());
crc32_ism.process_bytes(bytes.data(), GALILEO_ISM_CRC_DATA_BYTES);
const uint32_t crc_computed = crc32_ism.checksum();
std::bitset<96> extracted;
for (int32_t i = 0; i < GALILEO_ISM_CRC_DATA_BITS; ++i)
{
extracted[i] = bits[i + 32];
}
std::vector<uint8_t> data_bytes((extracted.size() + 7) / 8);
for (size_t i = 0; i < extracted.size(); i += 8)
{
uint8_t byte = 0;
for (size_t j = 0; j < 8 && i + j < extracted.size(); ++j)
{
byte |= (extracted[i + j] << j);
}
data_bytes[i / 8] = byte;
}
std::reverse(data_bytes.begin(), data_bytes.end());
const uint32_t crc_computed = this->compute_crc(data_bytes);
if (this->ism_crc == crc_computed)
{
return true;

2
src/core/system_parameters/galileo_ism.h
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@@ -69,10 +69,10 @@ public:
uint16_t get_WN_ISM() const;
uint16_t get_t0_ISM() const;
uint16_t get_Tvalidity_hours() const;
uint32_t compute_crc(const std::vector<uint8_t>& data);
private:
boost::crc_basic<32> crc32_ism;
uint32_t compute_crc(const std::vector<uint8_t>& data);
// ICD 2.1 Table 97
std::unordered_map<uint8_t, double> ISM_PCONST_MAP = {

2
src/tests/test_main.cc
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@@ -131,7 +131,7 @@ private:
#include "unit-tests/signal-processing-blocks/tracking/tracking_loop_filter_test.cc"
#include "unit-tests/system-parameters/galileo_e1b_reed_solomon_test.cc"
#include "unit-tests/system-parameters/galileo_e6b_reed_solomon_test.cc"
#include "unit-tests/system-parameters/glonass_gnav_crc_test.cc"
#include "unit-tests/system-parameters/galileo_ism_test.cc"
#include "unit-tests/system-parameters/glonass_gnav_ephemeris_test.cc"
#include "unit-tests/system-parameters/glonass_gnav_nav_message_test.cc"
#include "unit-tests/system-parameters/has_decoding_test.cc"

23
src/tests/unit-tests/system-parameters/galileo_ism_test.cc
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@@ -17,27 +17,14 @@
#include "galileo_ism.h"
#include <gtest/gtest.h>
#include <algorithm>
#include <bitset>
#include <vector>
TEST(GalileoISMTest, CRC)
{
// Example from ANNEX G Galileo ICD
Galileo_ISM gal_ism{};
uint32_t expected_crc = 3002390191;
std::bitset<96> input{"010110000010101010101010101010101010101010101010101010101010101010101010101010101010101010101010"};
std::vector<uint8_t> data_bytes;
for (size_t i = 0; i < input.size(); i += 8)
{
std::bitset<8> byte;
for (size_t j = 0; j < 8; j++)
{
byte[j] = input[i + j];
}
data_bytes.push_back(static_cast<uint8_t>(byte.to_ulong()));
}
std::reverse(data_bytes.begin(), data_bytes.end());
auto computed_crc = gal_ism.compute_crc(data_bytes);
EXPECT_TRUE(computed_crc == expected_crc);
gal_ism.set_ism_crc(expected_crc);
std::bitset<128> input{"01011000001010101010101010101010101010101010101010101010101010101010101010101010101010101010101010110010111101001101011010101111"};
bool result = gal_ism.check_ism_crc(input);
EXPECT_TRUE(result);
}