/*
    OWFS -- One-Wire filesystem
    OWHTTPD -- One-Wire Web Server
    Written 2003 Paul H Alfille
	email: paul.alfille@gmail.com
	Released under the GPL
	See the header file: ow.h for full attribution
	1wire/iButton system from Dallas Semiconductor
*/

#include <config.h>
#include "owfs_config.h"
#include "ow.h"
#include "ow_counters.h"

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

static UINT crc16_table[16] = { 0, 1, 1, 0, 1, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0 };

BYTE CRC8compute(const BYTE * bytes, const size_t length, const UINT seed)
{
	BYTE crc = seed;
	size_t i = 0;
	while (i < length) {
		crc = crc8_table[crc ^ bytes[i++]];
	}
	return crc;
}

/* wrap CRC8 calculation in statistics */
BYTE CRC8(const BYTE * bytes, const size_t length)
{
	return CRC8seeded(bytes, length, 0);
}

/* wrap CRC8 calculation in statistics */
BYTE CRC8seeded(const BYTE * bytes, const size_t length, const UINT seed)
{
	BYTE r = CRC8compute(bytes, length, seed);
	STATLOCK;
	++CRC8_tries;				/* statistics */
	if (r) {
		++CRC8_errors;			/* statistics */
	}
	STATUNLOCK;
	return r;
}

/* Returns 0 for good match */
/* Standard -- seed = 0 */
int CRC16(const BYTE * bytes, const size_t length)
{
	return CRC16seeded(bytes, length, 0);
}

/* Returns 0 for good match */
int CRC16seeded(const BYTE * bytes, const size_t length, const UINT seed)
{
	UINT sd = seed;
	int ret;
	size_t i;

	for (i = 0; i < length; ++i) {
		UINT c = (bytes[i] ^ (sd & 0xFF)) & 0xFF;
		sd >>= 8;
		if (crc16_table[c & 0x0F] ^ crc16_table[c >> 4]) {
			sd ^= 0xC001;
		}
		sd ^= (c <<= 6);
		sd ^= (c << 1);
	}
	STATLOCK;
	++CRC16_tries;				/* statistics */
	if (sd == 0xB001) {
		ret = 0;				/* good */
	} else {
		ret = -1;				/* error */
		++CRC16_errors;			/* statistics */
	}
	STATUNLOCK;
	return ret;
}
