LFN checksum for a given short file name in FAT32

checksum.c

#include <stdio.h>
#include <stdlib.h>

unsigned char
ChkSum (unsigned char *pFcbName)
{
  short FcbNameLen;
  unsigned char Sum;

  Sum = 0;                                                                                                                                                                                           
  for (FcbNameLen = 11; FcbNameLen != 0; FcbNameLen--)
    {   
      // NOTE: The operation is an unsigned char rotate right                 
      Sum = ((Sum & 1) ? 0x80 : 0) + (Sum >> 1) + *pFcbName++;
    }   
  return (Sum);
}

int
main (void)
{
  unsigned char SFN_old[11] =
    { 'T', 'H', 'I', 'S', 'I', 'S', '~', '1', ' ', ' ', ' ' };
  unsigned char SFN_new[11] =
    { 'M', 'Y', 'N', 'E', 'W', 'D', 'I', 'R', ' ', ' ', ' ' };
  unsigned char ck = ChkSum (SFN_old);
  printf ("Old Checksum=%X\n", ck);
  ck = ChkSum (SFN_new);
  printf ("New Checksum=%X\n", ck);
}