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CRC internal type more suitable for ARM.

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This commit is contained in:
Jared Boone 2016-02-18 21:31:51 -08:00
parent 00fb25f143
commit 1e0d34c98b
4 changed files with 35 additions and 25 deletions
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4
firmware/application/tpms_app.cpp
View file

@ -105,8 +105,8 @@ size_t Packet::crc_valid_length() const {
} }
uint32_t checksum = 0; uint32_t checksum = 0;
CRC<uint8_t> crc_72 { 0x01, 0x00 }; CRC<8> crc_72 { 0x01, 0x00 };
CRC<uint8_t> crc_80 { 0x01, 0x00 }; CRC<8> crc_80 { 0x01, 0x00 };
for(size_t i=0; i<bytes.size(); i++) { for(size_t i=0; i<bytes.size(); i++) {
const uint32_t byte_mask = 1 << i; const uint32_t byte_mask = 1 << i;

2
firmware/common/ais_packet.cpp
View file

@ -185,7 +185,7 @@ Longitude Packet::longitude(const size_t start_bit) const {
bool Packet::crc_ok() const { bool Packet::crc_ok() const {
CRCReader field_crc { packet_ }; CRCReader field_crc { packet_ };
CRC<uint16_t> ais_fcs { 0x1021, 0xffff, 0xffff }; CRC<16> ais_fcs { 0x1021, 0xffff, 0xffff };
for(size_t i=0; i<data_length(); i+=8) { for(size_t i=0; i<data_length(); i+=8) {
ais_fcs.process_byte(field_crc.read(i, 8)); ais_fcs.process_byte(field_crc.read(i, 8));

50
firmware/common/crc.hpp
View file

@ -24,6 +24,7 @@
#include <cstddef> #include <cstddef>
#include <cstdint> #include <cstdint>
#include <limits>
#include <array> #include <array>
/* Inspired by /* Inspired by
@ -39,13 +40,15 @@
* *
*/ */
template<typename T, bool RevIn = false, bool RevOut = false> template<size_t Width, bool RevIn = false, bool RevOut = false>
class CRC { class CRC {
public: public:
using value_type = uint32_t;
constexpr CRC( constexpr CRC(
const T truncated_polynomial, const value_type truncated_polynomial,
const T initial_remainder = 0, const value_type initial_remainder = 0,
const T final_xor_value = 0 const value_type final_xor_value = 0
) : truncated_polynomial { truncated_polynomial }, ) : truncated_polynomial { truncated_polynomial },
initial_remainder { initial_remainder }, initial_remainder { initial_remainder },
final_xor_value { final_xor_value }, final_xor_value { final_xor_value },
@ -53,11 +56,11 @@ public:
{ {
} }
T get_initial_remainder() const { value_type get_initial_remainder() const {
return initial_remainder; return initial_remainder;
} }
void reset(T new_initial_remainder) { void reset(value_type new_initial_remainder) {
remainder = new_initial_remainder; remainder = new_initial_remainder;
} }
@ -74,14 +77,17 @@ public:
} }
} }
void process_bits(uint8_t bits, size_t bit_count) { void process_bits(value_type bits, size_t bit_count) {
bits <<= (8 - bit_count); constexpr auto digits = std::numeric_limits<value_type>::digits;
constexpr auto mask = static_cast<value_type>(1) << (digits - 1);
bits <<= (std::numeric_limits<value_type>::digits - bit_count);
for(size_t i=bit_count; i>0; --i, bits <<= 1) { for(size_t i=bit_count; i>0; --i, bits <<= 1) {
process_bit(static_cast<bool>(bits & 0x80)); process_bit(static_cast<bool>(bits & mask));
} }
} }
void process_bits_lsb_first(uint8_t bits, size_t bit_count) { void process_bits_lsb_first(value_type bits, size_t bit_count) {
for(size_t i=bit_count; i>0; --i, bits >>= 1) { for(size_t i=bit_count; i>0; --i, bits >>= 1) {
process_bit(static_cast<bool>(bits & 0x01)); process_bit(static_cast<bool>(bits & 0x01));
} }
@ -106,26 +112,30 @@ public:
process_bytes(data.data(), data.size()); process_bytes(data.data(), data.size());
} }
T checksum() const { value_type checksum() const {
return (RevOut ? reflect(remainder) : remainder) ^ final_xor_value; return ((RevOut ? reflect(remainder) : remainder) ^ final_xor_value) & mask();
} }
private: private:
const T truncated_polynomial; const value_type truncated_polynomial;
const T initial_remainder; const value_type initial_remainder;
const T final_xor_value; const value_type final_xor_value;
T remainder; value_type remainder;
static constexpr size_t width() { static constexpr size_t width() {
return 8 * sizeof(T); return Width;
} }
static constexpr T top_bit() { static constexpr value_type top_bit() {
return 1U << (width() - 1); return 1U << (width() - 1);
} }
static T reflect(T x) { static constexpr value_type mask() {
T reflection = 0; return (~(~(0UL) << width()));
}
static value_type reflect(value_type x) {
value_type reflection = 0;
for(size_t i=0; i<width(); ++i) { for(size_t i=0; i<width(); ++i) {
reflection <<= 1; reflection <<= 1;
reflection |= (x & 1); reflection |= (x & 1);

4
firmware/common/ert_packet.cpp
View file

@ -76,7 +76,7 @@ bool Packet::crc_ok() const {
} }
bool Packet::crc_ok_scm() const { bool Packet::crc_ok_scm() const {
CRC<uint16_t> ert_bch { 0x6f63 }; CRC<16> ert_bch { 0x6f63 };
size_t start_bit = 5; size_t start_bit = 5;
ert_bch.process_byte(reader_.read(0, start_bit)); ert_bch.process_byte(reader_.read(0, start_bit));
for(size_t i=start_bit; i<length(); i+=8) { for(size_t i=start_bit; i<length(); i+=8) {
@ -86,7 +86,7 @@ bool Packet::crc_ok_scm() const {
} }
bool Packet::crc_ok_idm() const { bool Packet::crc_ok_idm() const {
CRC<uint16_t> ert_crc_ccitt { 0x1021, 0xffff, 0x1d0f }; CRC<16> ert_crc_ccitt { 0x1021, 0xffff, 0x1d0f };
for(size_t i=0; i<length(); i+=8) { for(size_t i=0; i<length(); i+=8) {
ert_crc_ccitt.process_byte(reader_.read(i, 8)); ert_crc_ccitt.process_byte(reader_.read(i, 8));
} }