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CRC class now supports reverse of input/output.

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This commit is contained in:
Jared Boone 2016-02-18 20:36:32 -08:00
parent c12833a288
commit 00fb25f143
1 changed files with 48 additions and 17 deletions
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65
firmware/common/crc.hpp
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@ -24,15 +24,22 @@
#include <cstddef> #include <cstddef>
#include <cstdint> #include <cstdint>
#include <array>
/* Inspired by /* Inspired by
* http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code * http://www.barrgroup.com/Embedded-Systems/How-To/CRC-Calculation-C-Code
* *
* ...then munged into a shape resembling boost::crc_basic. * ...then munged into a simplified implementation of boost::crc_basic and
* boost::crc_optimal.
* http://www.boost.org/doc/libs/release/libs/crc/ * http://www.boost.org/doc/libs/release/libs/crc/
*
* Copyright 2001, 2004 Daryle Walker. Use, modification, and distribution are
* subject to the Boost Software License, Version 1.0. (See accompanying file
* LICENSE_1_0.txt or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
*
*/ */
template<typename T> template<typename T, bool RevIn = false, bool RevOut = false>
class CRC { class CRC {
public: public:
constexpr CRC( constexpr CRC(
@ -59,22 +66,32 @@ public:
} }
void process_bit(bool bit) { void process_bit(bool bit) {
remainder ^= bit << (width() - 1); remainder ^= (bit ? top_bit() : 0U);
if( remainder & top_bit() ) { const auto do_poly_div = static_cast<bool>(remainder & top_bit());
remainder = (remainder << 1) ^ truncated_polynomial; remainder <<= 1;
} else { if( do_poly_div ) {
remainder = (remainder << 1); remainder ^= truncated_polynomial;
} }
} }
void process_byte(const uint8_t data) { void process_bits(uint8_t bits, size_t bit_count) {
remainder ^= data << (width() - 8); bits <<= (8 - bit_count);
for(size_t bit=0; bit<8; bit++) { for(size_t i=bit_count; i>0; --i, bits <<= 1) {
if( remainder & top_bit() ) { process_bit(static_cast<bool>(bits & 0x80));
remainder = (remainder << 1) ^ truncated_polynomial; }
} else { }
remainder = (remainder << 1);
} void process_bits_lsb_first(uint8_t bits, size_t bit_count) {
for(size_t i=bit_count; i>0; --i, bits >>= 1) {
process_bit(static_cast<bool>(bits & 0x01));
}
}
void process_byte(const uint8_t byte) {
if( RevIn ) {
process_bits_lsb_first(byte, 8);
} else {
process_bits(byte, 8);
} }
} }
@ -84,8 +101,13 @@ public:
} }
} }
template<size_t N>
void process_bytes(const std::array<uint8_t, N>& data) {
process_bytes(data.data(), data.size());
}
T checksum() const { T checksum() const {
return remainder ^ final_xor_value; return (RevOut ? reflect(remainder) : remainder) ^ final_xor_value;
} }
private: private:
@ -101,7 +123,16 @@ private:
static constexpr T top_bit() { static constexpr T top_bit() {
return 1U << (width() - 1); return 1U << (width() - 1);
} }
static T reflect(T x) {
T reflection = 0;
for(size_t i=0; i<width(); ++i) {
reflection <<= 1;
reflection |= (x & 1);
x >>= 1;
}
return reflection;
}
}; };
#endif/*__CRC_H__*/ #endif/*__CRC_H__*/