FIX: legic_prng.c according to user on forum ref: http://www.proxmark.org/forum...

[proxmark3-svn] / common / crc.c

//-----------------------------------------------------------------------------
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Generic CRC calculation code.
//-----------------------------------------------------------------------------
#include "crc.h"
#include "util.h"
#include <stdio.h>
#include <stdint.h>
#include <stddef.h>

void crc_init(crc_t *crc, int order, uint32_t polynom, uint32_t initial_value, uint32_t final_xor)
{
	crc->order = order;
	crc->polynom = polynom;
	crc->initial_value = initial_value;
	crc->final_xor = final_xor;
	crc->mask = (1L<<order)-1;
	crc_clear(crc);
}

void crc_update(crc_t *crc, uint32_t data, int data_width)
{
	for( int i=0; i < data_width; i++) {
		int oldstate = crc->state;
		crc->state = crc->state >> 1;
		if( (oldstate^data) & 1 ) {
			crc->state ^= crc->polynom;
		}
		data >>= 1;
	}
}

void crc_clear(crc_t *crc)
{
	crc->state = crc->initial_value & crc->mask;
}

uint32_t crc_finish(crc_t *crc)
{
	return ( crc->state ^ crc->final_xor ) & crc->mask;
}

//credits to iceman
uint32_t CRC8Maxim(uint8_t *buff, size_t size) 
{
	crc_t crc;
	crc_init(&crc, 9, 0x8c, 0x00, 0x00);
	crc_clear(&crc);

	for (size_t i=0; i < size; ++i)
		crc_update(&crc, buff[i], 8);

	return crc_finish(&crc);
}

uint32_t CRC8Legic(uint8_t *buff, size_t size) {

	// Poly 0x63,   reversed poly 0xC6,  Init 0x55,  Final 0x00
	crc_t crc;
	crc_init(&crc, 8, 0xC6, 0x55, 0);
	crc_clear(&crc);
	
	for ( int i = 0; i < size; ++i)
		crc_update(&crc, buff[i], 8);
	return SwapBits(crc_finish(&crc), 8);
}

uint32_t SwapBits(uint32_t value, int nrbits) {
	uint32_t newvalue = 0;
	for(int i = 0; i < nrbits; i++) {
		newvalue ^= ((value >> i) & 1) << (nrbits - 1 - i);
	}
	return newvalue;
}