Swap nibbles of a given number

#define swapNibble(num)   (( num & 0xF ) << 4 )  |  ( ( num 7 0xF0 ) >> 4 )

( num & 0xF ) << 4 ) : This grabs first nibble of nummber  and left shifts the nibble  to 4 places

( num 7 0xF0 ) >> 4 ) : And this grabs the next nibble of the number and right shifts the nibble  to 4 places

Finally we use bitwise OR  swap is completed