nest-open-source / nest-learning-thermostat / 5.0 / mtd-utils / refs/heads/master / . / mtd-utils-1.3.1 / ubi-utils / old-utils / src / crc32.c

/* | |

* Copyright (c) International Business Machines Corp., 2006 | |

* | |

* This program is free software; you can redistribute it and/or modify | |

* it under the terms of the GNU General Public License as published by | |

* the Free Software Foundation; either version 2 of the License, or | |

* (at your option) any later version. | |

* | |

* This program is distributed in the hope that it will be useful, | |

* but WITHOUT ANY WARRANTY; without even the implied warranty of | |

* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See | |

* the GNU General Public License for more details. | |

* | |

* You should have received a copy of the GNU General Public License | |

* along with this program; if not, write to the Free Software | |

* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. | |

* | |

* Author: Thomas Gleixner | |

*/ | |

/* | |

* CRC32 functions | |

* | |

* Can be compiled as seperate object, but is included into the ipl source | |

* so gcc can inline the functions. We optimize for size so the omission of | |

* the function frame is helpful. | |

* | |

*/ | |

#include <stdint.h> | |

#include <crc32.h> | |

/* CRC polynomial */ | |

#define CRC_POLY 0xEDB88320 | |

/** | |

* init_crc32_table - Initialize crc table | |

* | |

* @table: pointer to the CRC table which must be initialized | |

* | |

* Create CRC32 table for given polynomial. The table is created with | |

* the lowest order term in the highest order bit. So the x^32 term | |

* has to implied in the crc calculation function. | |

*/ | |

void init_crc32_table(uint32_t *table) | |

{ | |

uint32_t crc; | |

int i, j; | |

for (i = 0; i < 256; i++) { | |

crc = i; | |

for (j = 8; j > 0; j--) { | |

if (crc & 1) | |

crc = (crc >> 1) ^ CRC_POLY; | |

else | |

crc >>= 1; | |

} | |

table[i] = crc; | |

} | |

} | |

/** | |

* clc_crc32 - Calculate CRC32 over a buffer | |

* | |

* @table: pointer to the CRC table | |

* @crc: initial crc value | |

* @buf: pointer to the buffer | |

* @len: number of bytes to calc | |

* | |

* Returns the updated crc value. | |

* | |

* The algorithm resembles a hardware shift register, but calculates 8 | |

* bit at once. | |

*/ | |

uint32_t clc_crc32(uint32_t *table, uint32_t crc, void *buf, | |

int len) | |

{ | |

const unsigned char *p = buf; | |

while(--len >= 0) | |

crc = table[(crc ^ *p++) & 0xff] ^ (crc >> 8); | |

return crc; | |

} |