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/**
* \file
*
* \brief 32-bit CRC implementation.
*
* Copyright (C) 2014-2015 Atmel Corporation. All rights reserved.
*
* \asf_license_start
*
* \page License
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* 1. Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright notice,
* this list of conditions and the following disclaimer in the documentation
* and/or other materials provided with the distribution.
*
* 3. The name of Atmel may not be used to endorse or promote products derived
* from this software without specific prior written permission.
*
* 4. This software may only be redistributed and used in connection with an
* Atmel microcontroller product.
*
* THIS SOFTWARE IS PROVIDED BY ATMEL "AS IS" AND ANY EXPRESS OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT ARE
* EXPRESSLY AND SPECIFICALLY DISCLAIMED. IN NO EVENT SHALL ATMEL BE LIABLE FOR
* ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
* STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* \asf_license_stop
*
*/
/*
* Support and FAQ: visit <a href="http://www.atmel.com/design-support/">Atmel Support</a>
*/
#include "crc32.h"
#include <status_codes.h>
/**
* Convenience typedef for words.
*
* \note This type has an architecture dependent size, and is used to optimize
* the CRC algorithm with regards to the number of databus accesses.
*/
typedef unsigned int word_t;
/** Polynomial for 32-bit CRC in IEEE 802.3. */
#define CRC32_POLYNOMIAL 0xEDB88320UL
/** Convenience macro for inverting the CRC. */
#define COMPLEMENT_CRC(c) ((c) ^ 0xffffffffUL)
/** Convenience macro for size of a word. */
#define WORD_SIZE (sizeof(word_t))
/** Bitmask for word-aligning an address. */
#define WORD_ALIGNMENT_MASK ~((uintptr_t)WORD_SIZE - 1)
/**
* \internal
* \brief Recalculate 32-bit CRC for bytes within a word
*
* \param[in] data Data to recalculate for.
* \param[in] crc Initial/current CRC value.
* \param[in] bytes Number of data bytes in word.
*
* \return New CRC value.
*
* \attention This implementation assumes a little-endian architecture.
*/
static inline crc32_t _crc32_recalculate_bytes_helper(word_t data,
crc32_t crc, uint_fast8_t bytes)
{
uint_fast8_t bit;
crc ^= data;
for (bit = 8 * bytes; bit > 0; bit--) {
if (crc & 1) {
crc = (crc >> 1) ^ CRC32_POLYNOMIAL;
} else {
crc >>= 1;
}
}
return crc;
}
/**
* \brief Recalculate 32-bit CRC for another block
*
* This function recalculates the CRC according to the polynomial
* \ref CRC32_POLYNOMIAL for the specified data block and initial CRC value.
*
* To reduce the number of databus accesses and thus speed up the calculation,
* the algorithm is tuned to work with words as much as possible.
*
* \param[in] data Address of data.
* \param[in] length Length of data.
* \param[in,out] crc Address of variable containing current CRC, and to store
* recalculated CRC in.
*
* \return Status of calculation.
* \retval STATUS_OK if calculation succeeded.
* \retval <other> if calculation failed or could not be started.
*
* \note To calculate the CRC of multiple blocks, use \ref crc32_calculate()
* first, then this function for the following blocks.
*
* \attention This implementation assumes a little-endian architecture.
*/
enum status_code crc32_recalculate(const void *data, size_t length, crc32_t *crc)
{
const word_t *word_ptr =
(word_t *)((uintptr_t)data & WORD_ALIGNMENT_MASK);
size_t temp_length;
crc32_t temp_crc = COMPLEMENT_CRC(*crc);
word_t word;
// Calculate for initial bytes to get word-aligned
if (length < WORD_SIZE) {
temp_length = length;
} else {
temp_length = ~WORD_ALIGNMENT_MASK & (WORD_SIZE - (uintptr_t)data);
}
if (temp_length) {
length -= temp_length;
word = *(word_ptr++);
word >>= 8 * (WORD_SIZE - temp_length);
temp_crc = _crc32_recalculate_bytes_helper(word, temp_crc, temp_length);
}
// Calculate for whole words, if any
temp_length = length & WORD_ALIGNMENT_MASK;
if (temp_length) {
length -= temp_length;
temp_length /= WORD_SIZE;
while (temp_length--) {
word = *(word_ptr++);
temp_crc = _crc32_recalculate_bytes_helper(word, temp_crc, WORD_SIZE);
}
}
// Calculate for tailing bytes
if (length) {
word = *word_ptr;
word &= 0xffffffffUL >> (8 * (WORD_SIZE - length));
temp_crc = _crc32_recalculate_bytes_helper(word, temp_crc, length);
}
*crc = COMPLEMENT_CRC(temp_crc);
return STATUS_OK;
}
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