crc16.cpp

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// This code came from the AutoPilot Manual
// it should be replaced with the boost version if possible

#include "asctec_autopilot/crc16.h"

namespace asctec
{

  bool crc_valid (unsigned short packet_crc, void *data, unsigned short cnt)
  {
    unsigned short checksum = crc16 (data, cnt);

    if (checksum == packet_crc)
    {
      return true;
    }
    return false;
  }

  unsigned short crc_update (unsigned short crc, unsigned char data)
  {
    data ^= (crc & 0xff);
    data ^= data << 4;

    return ((((unsigned short) data << 8) | ((crc >> 8) & 0xff)) ^ (unsigned char) (data >> 4)
            ^ ((unsigned short) data << 3));
  }

  unsigned short crc16 (void *data, unsigned short cnt)
  {
    unsigned short crc = 0xff;
    unsigned char *ptr = (unsigned char *) data;
    int i;

    for (i = 0; i < cnt; i++)
    {
      crc = crc_update (crc, *ptr);
      ptr++;
    }
    return crc;
  }
}