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/**********************************************************************
 *
 * Filename:    ci_crc.c
 * 
 * Description: Custom instruction implementations of the CRC.
 *
 * Notes:       A macro is defined that is used to access the CRC custom  
 *              instruction.
 *********************************************************************/
 
#include "system.h"

/*The n values and their corresponding operation are as follow:
 * n = 0, Initialize the custom instruction to the initial remainder value
 * n = 1, Write  8 bits data to custom instruction
 * n = 2, Write 16 bits data to custom instruction
 * n = 3, Write 32 bits data to custom instruction
 * n = 4, Read  32 bits data from the custom instruction
 * n = 5, Read  64 bits data from the custom instruction
 * n = 6, Read  96 bits data from the custom instruction
 * n = 7, Read 128 bits data from the custom instruction*/
#define CRC_CI_MACRO(n, A)        __builtin_custom_ini(ALT_CI_NIOS2_HW_CRC32_0_N + (n & 0x7), (A))

unsigned long crcCI(unsigned char * input_data, unsigned long input_data_length, int do_initialize)
{
  unsigned long index;
  /* copy of the data buffer pointer so that it can advance by different widths */
  void * input_data_copy = (void *)input_data;

  /* The custom instruction CRC will initialize to the inital remainder value */    
  if (do_initialize)
    CRC_CI_MACRO(0,0);
  
  /* Write 32 bit data to the custom instruction.  If the buffer does not end
   * on a 32 bit boundary then the remaining data will be sent to the custom
   * instruction in the 'if' statement below.
   */
  for(index = 0; index < (input_data_length & 0xFFFFFFFC); index+=4)
  {
    CRC_CI_MACRO(3, *(unsigned long *)input_data_copy);
    input_data_copy += 4;  /* void pointer, must move by 4 for each word */
  }

  /* Write the remainder of the buffer if it does not end on a word boundary */  
  if((input_data_length & 0x3) == 0x3)  /* 3 bytes left */
  {
    CRC_CI_MACRO(2, *(unsigned short *)input_data_copy);
    input_data_copy += 2;
    CRC_CI_MACRO(1, *(unsigned char *)input_data_copy);
  }
  else if((input_data_length & 0x3) == 0x2) /* 2 bytes left */
  {
    CRC_CI_MACRO(2, *(unsigned short *)input_data_copy);    
  }
  else if((input_data_length & 0x3) == 0x1) /* 1 byte left */
  {
    CRC_CI_MACRO(1, *(unsigned char *)input_data_copy);    
  }
  
  /* There are 4 registers in the CRC custom instruction.  Since
   * this example uses CRC-32 only the first register must be read
   * in order to receive the full result.
   */
  return CRC_CI_MACRO(4, 0);
}