132 lines
3.4 KiB
C
132 lines
3.4 KiB
C
/*
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* Library: libcrc
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* File: src/crc32.c
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* Author: Lammert Bies
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*
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* This file is licensed under the MIT License as stated below
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*
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* Copyright (c) 1999-2016 Lammert Bies
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in all
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* copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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* SOFTWARE.
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*
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* Description
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* -----------
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* The source file src/crc32.c contains the routines which are needed to
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* calculate a 32 bit CRC value of a sequence of bytes.
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*/
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#include <stdbool.h>
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#include <stdlib.h>
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#include "checksum.h"
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static void init_crc32_tab( void );
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static bool crc_tab32_init = false;
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static uint32_t crc_tab32[256];
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/*
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* uint32_t crc_32( const unsigned char *input_str, size_t num_bytes );
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*
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* The function crc_32() calculates in one pass the common 32 bit CRC value for
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* a byte string that is passed to the function together with a parameter
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* indicating the length.
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*/
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uint32_t crc_32( const unsigned char *input_str, size_t num_bytes ) {
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uint32_t crc;
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uint32_t tmp;
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uint32_t long_c;
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const unsigned char *ptr;
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size_t a;
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if ( ! crc_tab32_init ) init_crc32_tab();
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crc = CRC_START_32;
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ptr = input_str;
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if ( ptr != NULL ) for (a=0; a<num_bytes; a++) {
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long_c = 0x000000FFL & (uint32_t) *ptr;
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tmp = crc ^ long_c;
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crc = (crc >> 8) ^ crc_tab32[ tmp & 0xff ];
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ptr++;
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}
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crc ^= 0xffffffffL;
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return crc & 0xffffffffL;
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} /* crc_32 */
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/*
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* uint32_t update_crc_32( uint32_t crc, unsigned char c );
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*
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* The function update_crc_32() calculates a new CRC-32 value based on the
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* previous value of the CRC and the next byte of the data to be checked.
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*/
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uint32_t update_crc_32( uint32_t crc, unsigned char c ) {
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uint32_t tmp;
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uint32_t long_c;
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long_c = 0x000000ffL & (uint32_t) c;
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if ( ! crc_tab32_init ) init_crc32_tab();
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tmp = crc ^ long_c;
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crc = (crc >> 8) ^ crc_tab32[ tmp & 0xff ];
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return crc & 0xffffffffL;;
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} /* update_crc_32 */
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/*
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* static void init_crc32_tab( void );
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*
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* For optimal speed, the CRC32 calculation uses a table with pre-calculated
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* bit patterns which are used in the XOR operations in the program. This table
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* is generated once, the first time the CRC update routine is called.
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*/
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static void init_crc32_tab( void ) {
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uint32_t i;
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uint32_t j;
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uint32_t crc;
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for (i=0; i<256; i++) {
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crc = i;
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for (j=0; j<8; j++) {
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if ( crc & 0x00000001L ) crc = ( crc >> 1 ) ^ CRC_POLY_32;
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else crc = crc >> 1;
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}
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crc_tab32[i] = crc;
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}
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crc_tab32_init = true;
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} /* init_crc32_tab */
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