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Merge pull request #21543 from crasbe/pr/crc8_refl

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sys/checksum: Add LSB-first (reflected) CRC8 Function
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crasbe 2025-06-07 12:07:11 +00:00 committed by GitHub
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7 changed files with 169 additions and 38 deletions
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17
sys/checksum/crc8.c
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@ -39,4 +39,21 @@ uint8_t crc8(const uint8_t *data, size_t len, uint8_t g_polynom, uint8_t crc)
return crc;
}
uint8_t crc8_lsb(const uint8_t *data, size_t len, uint8_t g_polynom, uint8_t crc)
{
for (size_t i = 0; i < len; i++)
{
crc ^= data[i];
for (int i = 0; i < 8; i++)
{
bool xor = crc & 0x01;
crc = crc >> 1;
crc = xor ? crc ^ g_polynom : crc;
}
}
return crc;
}
/** @} */

33
sys/checksum/doc.md Normal file
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@ -0,0 +1,33 @@
<!--
Copyright 2016 Freie Universität Berlin
Copyright 2016 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
This file is subject to the terms and conditions of the GNU Lesser
General Public License v2.1. See the file LICENSE in the top level
directory for more details.
-->
@defgroup sys_checksum Checksum
@ingroup sys_hashes
@brief Checksum function libraries
This module provides a number of checksum functions. Most notably is the
@ref sys_checksum_crc16_ccitt and the @ref sys_checksum_ucrc16 modules which
provide support for the CRC16 checksum.
@ref sys_checksum_crc16_ccitt only provides an implementation of the CCITT
flavor of CRC16 (polynomial @$ x^{16} + x^{12} + x^{5} + 1 @$) for big-endian
numbers with starting seed `0x1d0f` (though others can be provided), while
@ref sys_checksum_ucrc16 is more generalized, since it takes the
hexadecimal representation of the polynomial as a parameter and provides
functions and standardized polynomials for both big- and little-endian
numbers.
The caveat of @ref sys_checksum_ucrc16 is that it is significantly slower
(approximately factor 8) than @ref sys_checksum_crc16_ccitt since the latter
is able to calculate the checksum byte-wise, while the first calculates
needs to calculate it bit-wise. @ref sys_checksum_crc16_ccitt achieves this
advantage by using a look-up table that provides the checksum for every
possible byte-value. It thus trades of memory against speed. If your
platform is rather small equipped in memory you should prefer the
@ref sys_checksum_ucrc16 version.

35
sys/checksum/doc.txt
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@ -1,35 +0,0 @@
/*
* Copyright 2016 Freie Universität Berlin
* Copyright 2016 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
/**
* @defgroup sys_checksum Checksum
* @ingroup sys_hashes
* @brief Checksum function libraries
*
* This module provides a number of checksum functions. Most notably is the
* @ref sys_checksum_crc16_ccitt and the @ref sys_checksum_ucrc16 modules which
* provide support for the CRC16 checksum.
*
* @ref sys_checksum_crc16_ccitt only provides an implementation of the CCITT
* flavor of CRC16 (polynomial @$ x^{16} + x^{12} + x^{5} + 1 @$) for big-endian
* numbers with starting seed `0x1d0f` (though others can be provided), while
* @ref sys_checksum_ucrc16 is more generalized, since it takes the
* hexadecimal representation of the polynomial as a parameter and provides
* functions and standardized polynomials for both big- and little-endian
* numbers.
*
* The caveat of @ref sys_checksum_ucrc16 is that it is significantly slower
* (approximately factor 8) than @ref sys_checksum_crc16_ccitt since the latter
* is able to calculate the checksum byte-wise, while the first calculates
* needs to calculate it bit-wise. @ref sys_checksum_crc16_ccitt achieves this
* advantage by using a look-up table that provides the checksum for every
* possible byte-value. It thus trades of memory against speed. If your
* platform is rather small equipped in memory you should prefer the
* @ref sys_checksum_ucrc16 version.
*/

23
sys/include/checksum/crc8.h
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@ -29,20 +29,37 @@ extern "C" {
#endif
/**
* @brief Calculate CRC-8
* @brief Calculate CRC-8 (MSB first)
*
* This CRC8 checksum type is usually more common.
*
* @param[in] data Start of memory area to checksum
* @param[in] len Number of bytes in @p buf to calculate checksum for
* @param[in] poly The generator polynomial for the checksum
* @param[in] seed The seed (starting value) for the checksum
*
* @note Reflected inputs or outputs and final XOR must be realized
* by the caller if needed.
* @note A final XOR must be realized by the caller if needed.
*
* @return Checksum of the specified memory area.
*/
uint8_t crc8(const uint8_t *data, size_t len, uint8_t poly, uint8_t seed);
/**
* @brief Calculate a reflected CRC-8 (LSB first)
*
* This CRC8 checksum type is used for example by Onewire.
*
* @param[in] data Start of memory area to checksum
* @param[in] len Number of bytes in @p buf to calculate checksum for
* @param[in] poly The generator polynomial for the checksum
* @param[in] seed The seed (starting value) for the checksum
*
* @note A final XOR must be realized by the caller if needed.
*
* @return Checksum of the specified memory area.
*/
uint8_t crc8_lsb(const uint8_t *data, size_t len, uint8_t poly, uint8_t seed);
#ifdef __cplusplus
}
#endif

91
tests/unittests/tests-checksum/tests-checksum-crc8-lsb.c Normal file
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@ -0,0 +1,91 @@
/*
* Copyright 2019 Benjamin Valentin <benpicco@googlemail.com>
*
* This file is subject to the terms and conditions of the GNU Lesser
* General Public License v2.1. See the file LICENSE in the top level
* directory for more details.
*/
#include <stdint.h>
#include "embUnit/embUnit.h"
#include "checksum/crc8.h"
#include "tests-checksum.h"
#define CRC8_POLY 0x31
#define CRC8_INIT 0xff
static void test_checksum_crc8_lsb_sequence_empty(void)
{
unsigned char buf[] = "";
uint8_t expect = 0xFF;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf) - 1, CRC8_POLY, CRC8_INIT));
}
static void test_checksum_crc8_lsb_sequence_1a(void)
{
unsigned char buf[] = "A";
uint8_t expect = 0x0F;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf) - 1, CRC8_POLY, CRC8_INIT));
}
static void test_checksum_crc8_lsb_sequence_256a(void)
{
unsigned char buf[] = "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"
"AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA";
uint8_t expect = 0x0F;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf) - 1, CRC8_POLY, CRC8_INIT));
}
static void test_checksum_crc8_lsb_sequence_1to9(void)
{
unsigned char buf[] = "123456789";
uint8_t expect = 0x20;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf) - 1, CRC8_POLY, CRC8_INIT));
}
static void test_checksum_crc8_lsb_sequence_4bytes(void)
{
unsigned char buf[] = { 0x12, 0x34, 0x56, 0x78 };
uint8_t expect = 0x1C;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf), CRC8_POLY, CRC8_INIT));
}
static void test_checksum_crc8_lsb_onewire_params(void)
{
unsigned char buf[] = { 0x2A };
uint8_t expect = 0x5D;
TEST_ASSERT_EQUAL_INT(expect, crc8_lsb(buf, sizeof(buf), 0x8C, 0x00));
}
Test *tests_checksum_crc8_lsb_tests(void)
{
EMB_UNIT_TESTFIXTURES(fixtures) {
/* Reference values according to
* http://srecord.sourceforge.net/crc16-ccitt.html */
new_TestFixture(test_checksum_crc8_lsb_sequence_empty),
new_TestFixture(test_checksum_crc8_lsb_sequence_1a),
new_TestFixture(test_checksum_crc8_lsb_sequence_256a),
new_TestFixture(test_checksum_crc8_lsb_sequence_1to9),
new_TestFixture(test_checksum_crc8_lsb_sequence_4bytes),
new_TestFixture(test_checksum_crc8_lsb_onewire_params),
};
EMB_UNIT_TESTCALLER(checksum_crc8_lsb_tests, NULL, NULL, fixtures);
return (Test *)&checksum_crc8_lsb_tests;
}

1
tests/unittests/tests-checksum/tests-checksum.c
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@ -11,6 +11,7 @@
void tests_checksum(void)
{
TESTS_RUN(tests_checksum_crc8_tests());
TESTS_RUN(tests_checksum_crc8_lsb_tests());
TESTS_RUN(tests_checksum_crc16_ccitt_kermit_tests());
TESTS_RUN(tests_checksum_crc16_ccitt_mcrf4xx_tests());
TESTS_RUN(tests_checksum_crc16_ccitt_aug_tests());

7
tests/unittests/tests-checksum/tests-checksum.h
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@ -36,6 +36,13 @@ void tests_checksum(void);
*/
Test *tests_checksum_crc8_tests(void);
/**
* @brief Generates tests for checksum/crc8_lsb.h
*
* @return embUnit tests if successful, NULL if not.
*/
Test *tests_checksum_crc8_lsb_tests(void);
/**
* @brief Generates tests for crc16-ccitt-kermit from checksum/crc16_ccitt.h
*