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