//-----------------------------------------------------------------------------
// 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.
//-----------------------------------------------------------------------------
// ISO15693 CRC & other commons
//-----------------------------------------------------------------------------

#include "iso15693tools.h"

// The CRC as described in ISO 15693-Part 3-Annex C
// 	v	buffer with data
//		n	length
//	returns crc as 16bit value
uint16_t Iso15693Crc(uint8_t *v, int n)
{
	uint32_t reg;
	int i, j;

	reg = 0xffff;
	for(i = 0; i < n; i++) {
		reg = reg ^ ((uint32_t)v[i]);
		for (j = 0; j < 8; j++) {
			if (reg & 0x0001) {
				reg = (reg >> 1) ^ 0x8408;
			} else {
				reg = (reg >> 1);
			}
		}
	}

	return ~(uint16_t)(reg & 0xffff);
}

// adds a CRC to a dataframe
// 	req[]   iso15963 frame without crc
//		n       length without crc
// returns the new length of the dataframe.
int Iso15693AddCrc(uint8_t *req, int n) {
	uint16_t crc=Iso15693Crc(req,n);
	req[n] = crc & 0xff;
	req[n+1] = crc >> 8;
	return n+2;
}

int sprintf(char *str, const char *format, ...);

// returns a string representation of the UID
// UID is transmitted and stored LSB first, displayed MSB first
//		target    char* buffer, where to put the UID, if NULL a static buffer is returned
//		uid[]		the UID in transmission order
//	return: ptr to string
char* Iso15693sprintUID(char *target, uint8_t *uid) {

	static char tempbuf[2*8+1] = {0};
	if (target == NULL) 
		target = tempbuf;
	sprintf(target, "%02X %02X %02X %02X %02X %02X %02X %02X",
				uid[7], uid[6], uid[5], uid[4],
				uid[3], uid[2], uid[1], uid[0]
	);
	return target;
}

uint16_t iclass_crc16(char *data_p, unsigned short length)
{
      unsigned char i;
      unsigned int data;
	  uint16_t crc = 0xffff;

      if (length == 0)
            return (~crc);

      do
      {
            for (i=0, data=(unsigned int)0xff & *data_p++;
                 i < 8; 
                 i++, data >>= 1)
            {
                  if ((crc & 0x0001) ^ (data & 0x0001))
                        crc = (crc >> 1) ^ POLY;
                  else  crc >>= 1;
            }
      } while (--length);

      crc = ~crc;
      data = crc;
      crc = (crc << 8) | (data >> 8 & 0xff);
      crc = crc ^ 0xBC3;
      return (crc);
}