ARM7 REV RBIT REV16

// Reverse the bit order in a 32-bit word.
unsigned int rbit(
  unsigned int i )
{
  i = ( ( i & 0x55555555 ) << 1 ) | ( ( i >> 1 ) & 0x55555555 );
  i = ( ( i & 0x33333333 ) << 2 ) | ( ( i >> 2 ) & 0x33333333 );
  i = ( ( i & 0x0f0f0f0f ) << 4 ) | ( ( i >> 4 ) & 0x0f0f0f0f );
  i = ( i << 24 ) | ( ( i & 0xff00 ) << 8 ) //
    | ( ( i >> 8 ) & 0xff00 ) | ( i >> 24 );
  return i;
}

// Reverse byte order in each halfword independently
// converts 16-bit big-endian data into little-endian data
// or 16-bit little-endian data into big-endian data
short rev16(
  short s )
{
  return ( s << 8 ) | ( s >> 8 );
}

// Reverse byte order in a word
// converts 32-bit big-endian data into little-endian data
// or 32-bit little-endian data into big-endian data.
unsigned int rev(
  unsigned int i )
{
  return ( i & 0x000000FFU ) << 24 | ( i & 0x0000FF00U ) << 8
    | ( i & 0x00FF0000U ) >> 8 | ( i & 0xFF000000U ) >> 24;
}