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Linux/lib/crc8.c

  1 /*
  2  * Copyright (c) 2011 Broadcom Corporation
  3  *
  4  * Permission to use, copy, modify, and/or distribute this software for any
  5  * purpose with or without fee is hereby granted, provided that the above
  6  * copyright notice and this permission notice appear in all copies.
  7  *
  8  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  9  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 10  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 11  * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 12  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 13  * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 14  * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 15  */
 16 
 17 #define pr_fmt(fmt)             KBUILD_MODNAME ": " fmt
 18 
 19 #include <linux/module.h>
 20 #include <linux/crc8.h>
 21 #include <linux/printk.h>
 22 
 23 /*
 24  * crc8_populate_msb - fill crc table for given polynomial in reverse bit order.
 25  *
 26  * table:       table to be filled.
 27  * polynomial:  polynomial for which table is to be filled.
 28  */
 29 void crc8_populate_msb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)
 30 {
 31         int i, j;
 32         const u8 msbit = 0x80;
 33         u8 t = msbit;
 34 
 35         table[0] = 0;
 36 
 37         for (i = 1; i < CRC8_TABLE_SIZE; i *= 2) {
 38                 t = (t << 1) ^ (t & msbit ? polynomial : 0);
 39                 for (j = 0; j < i; j++)
 40                         table[i+j] = table[j] ^ t;
 41         }
 42 }
 43 EXPORT_SYMBOL(crc8_populate_msb);
 44 
 45 /*
 46  * crc8_populate_lsb - fill crc table for given polynomial in regular bit order.
 47  *
 48  * table:       table to be filled.
 49  * polynomial:  polynomial for which table is to be filled.
 50  */
 51 void crc8_populate_lsb(u8 table[CRC8_TABLE_SIZE], u8 polynomial)
 52 {
 53         int i, j;
 54         u8 t = 1;
 55 
 56         table[0] = 0;
 57 
 58         for (i = (CRC8_TABLE_SIZE >> 1); i; i >>= 1) {
 59                 t = (t >> 1) ^ (t & 1 ? polynomial : 0);
 60                 for (j = 0; j < CRC8_TABLE_SIZE; j += 2*i)
 61                         table[i+j] = table[j] ^ t;
 62         }
 63 }
 64 EXPORT_SYMBOL(crc8_populate_lsb);
 65 
 66 /*
 67  * crc8 - calculate a crc8 over the given input data.
 68  *
 69  * table: crc table used for calculation.
 70  * pdata: pointer to data buffer.
 71  * nbytes: number of bytes in data buffer.
 72  * crc: previous returned crc8 value.
 73  */
 74 u8 crc8(const u8 table[CRC8_TABLE_SIZE], u8 *pdata, size_t nbytes, u8 crc)
 75 {
 76         /* loop over the buffer data */
 77         while (nbytes-- > 0)
 78                 crc = table[(crc ^ *pdata++) & 0xff];
 79 
 80         return crc;
 81 }
 82 EXPORT_SYMBOL(crc8);
 83 
 84 MODULE_DESCRIPTION("CRC8 (by Williams, Ross N.) function");
 85 MODULE_AUTHOR("Broadcom Corporation");
 86 MODULE_LICENSE("Dual BSD/GPL");
 87 

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