#include "nvram.h"

/*******************************************************************************
 * crc8
 *
 * Computes a crc8 over the input data using the polynomial:
 *
 *       x^8 + x^7 +x^6 + x^4 + x^2 + 1
 *
 * The caller provides the initial value (either CRC8_INIT_VALUE
 * or the previous returned value) to allow for processing of
 * discontiguous blocks of data.  When generating the CRC the
 * caller is responsible for complementing the final return value
 * and inserting it into the byte stream.  When checking, a final
 * return value of CRC8_GOOD_VALUE indicates a valid CRC.
 *
 * Reference: Dallas Semiconductor Application Note 27
 *   Williams, Ross N., "A Painless Guide to CRC Error Detection Algorithms",
 *     ver 3, Aug 1993, ross@guest.adelaide.edu.au, Rocksoft Pty Ltd.,
 *     ftp://ftp.rocksoft.com/clients/rocksoft/papers/crc_v3.txt
 *
 * ****************************************************************************
 */

static const uint8_t crc8_table[256] = {
	0x00, 0xF7, 0xB9, 0x4E, 0x25, 0xD2, 0x9C, 0x6B,
	0x4A, 0xBD, 0xF3, 0x04, 0x6F, 0x98, 0xD6, 0x21,
	0x94, 0x63, 0x2D, 0xDA, 0xB1, 0x46, 0x08, 0xFF,
	0xDE, 0x29, 0x67, 0x90, 0xFB, 0x0C, 0x42, 0xB5,
	0x7F, 0x88, 0xC6, 0x31, 0x5A, 0xAD, 0xE3, 0x14,
	0x35, 0xC2, 0x8C, 0x7B, 0x10, 0xE7, 0xA9, 0x5E,
	0xEB, 0x1C, 0x52, 0xA5, 0xCE, 0x39, 0x77, 0x80,
	0xA1, 0x56, 0x18, 0xEF, 0x84, 0x73, 0x3D, 0xCA,
	0xFE, 0x09, 0x47, 0xB0, 0xDB, 0x2C, 0x62, 0x95,
	0xB4, 0x43, 0x0D, 0xFA, 0x91, 0x66, 0x28, 0xDF,
	0x6A, 0x9D, 0xD3, 0x24, 0x4F, 0xB8, 0xF6, 0x01,
	0x20, 0xD7, 0x99, 0x6E, 0x05, 0xF2, 0xBC, 0x4B,
	0x81, 0x76, 0x38, 0xCF, 0xA4, 0x53, 0x1D, 0xEA,
	0xCB, 0x3C, 0x72, 0x85, 0xEE, 0x19, 0x57, 0xA0,
	0x15, 0xE2, 0xAC, 0x5B, 0x30, 0xC7, 0x89, 0x7E,
	0x5F, 0xA8, 0xE6, 0x11, 0x7A, 0x8D, 0xC3, 0x34,
	0xAB, 0x5C, 0x12, 0xE5, 0x8E, 0x79, 0x37, 0xC0,
	0xE1, 0x16, 0x58, 0xAF, 0xC4, 0x33, 0x7D, 0x8A,
	0x3F, 0xC8, 0x86, 0x71, 0x1A, 0xED, 0xA3, 0x54,
	0x75, 0x82, 0xCC, 0x3B, 0x50, 0xA7, 0xE9, 0x1E,
	0xD4, 0x23, 0x6D, 0x9A, 0xF1, 0x06, 0x48, 0xBF,
	0x9E, 0x69, 0x27, 0xD0, 0xBB, 0x4C, 0x02, 0xF5,
	0x40, 0xB7, 0xF9, 0x0E, 0x65, 0x92, 0xDC, 0x2B,
	0x0A, 0xFD, 0xB3, 0x44, 0x2F, 0xD8, 0x96, 0x61,
	0x55, 0xA2, 0xEC, 0x1B, 0x70, 0x87, 0xC9, 0x3E,
	0x1F, 0xE8, 0xA6, 0x51, 0x3A, 0xCD, 0x83, 0x74,
	0xC1, 0x36, 0x78, 0x8F, 0xE4, 0x13, 0x5D, 0xAA,
	0x8B, 0x7C, 0x32, 0xC5, 0xAE, 0x59, 0x17, 0xE0,
	0x2A, 0xDD, 0x93, 0x64, 0x0F, 0xF8, 0xB6, 0x41,
	0x60, 0x97, 0xD9, 0x2E, 0x45, 0xB2, 0xFC, 0x0B,
	0xBE, 0x49, 0x07, 0xF0, 0x9B, 0x6C, 0x22, 0xD5,
	0xF4, 0x03, 0x4D, 0xBA, 0xD1, 0x26, 0x68, 0x9F
};

uint8_t hndcrc8 (
	uint8_t * pdata,  /* pointer to array of data to process */
	uint32_t nbytes,  /* number of input data bytes to process */
	uint8_t crc       /* either CRC8_INIT_VALUE or previous return value */
) {
	while (nbytes-- > 0)
		crc = crc8_table[(crc ^ *pdata++) & 0xff];

	return crc;
}
