crc.cpp

/***********************************************************************************
    Filename: crc.cpp

    Copyright 2008 Texas Instruments, Inc.
***********************************************************************************/

#include "crc.hpp"

//-------------------------------------------------------------------------------------------------------
//  uint16_t crcCalc(uint16_t crcReg, uint8_t crcData) 
//
//  DESCRIPTION:
//      Calculates the 16-bit CRC. The function requires that the CRC_POLYNOM is defined,
//      which gives the wanted CRC polynom. 
//
//  ARGUMENTS: 
//      uint8_t  crcData  - Data to perform the CRC-16 operation on.
//      uint16_t crcReg   - Current or initial value of the CRC calculation
//
//  RETURN:
//      The value returned is the 16-bit CRC (of the data supplied so far). 
//-------------------------------------------------------------------------------------------------------
uint16_t crcCalc(uint16_t crcReg, uint8_t crcData) 
{
  uint8_t i;

  for (i = 0; i < 8; i++) {
    // If upper most bit is 1
    if (((crcReg & 0x8000) >> 8) ^ (crcData & 0x80)) {
      crcReg = (crcReg << 1)  ^ CRC_POLYNOM;
    }
    else {
      crcReg = (crcReg << 1);
    }

    crcData <<= 1;
  }

  return crcReg;
}


//-------------------------------------------------------------------------------------------------------
//  uint8_t crcRemove(uint8_t *data, uint8_t dataLen)
//
//  DESCRIPTION:
//      Remove CRC from data buffer 
//
//  ARGUMENTS: 
//      uint8_t*  data  - Data to perform the CRC remove operation on.
//      uint8_t dataLen - Current data length in buffer.
//
//  RETURN:
//      New data length in buffer.
//-------------------------------------------------------------------------------------------------------
uint8_t crcRemove(uint8_t *data, uint8_t dataLen)
{
  uint8_t *dst = data;
  uint8_t dstLen = 0;

  dst += 10;
  dstLen += 10;

  data += 12;
  dataLen -= 12;

  while (dataLen) {
    if (dataLen >= 18) {
      memmove(dst, data, 16);

      dst += 16;
      dstLen += 16;

      data += 18;
      dataLen -= 18;
    }
    else {
      memmove(dst, data, dataLen-2);

      dst += (dataLen-2);
      dstLen += (dataLen-2);

      data += dataLen;
      dataLen -= dataLen;
    }
  }
  return dstLen;
}


/***********************************************************************************
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***********************************************************************************/