Delphi in a Nutshell

Name

Swap Function

Syntax

function Swap(Value: Integer): Integer;

Description

The Swap function swaps the bytes in the least significant word of Value. It leaves the high order 16 bits alone. If Value is of type Int64, Swap silently ignores the most significant 32 bits, leaves the next most significant 16 bits alone, and performs the swap of the low order 16 bits. It returns the resulting 32-bit value (having discarded completely the original high-order 32 bits).

Swap is not a real function, but is expanded inline.

Tips and Tricks

• This function is provided for backward compatibility. It has little use in its current incarnation.

• Swapping bytes is a common activity when moving files or data through a network. Intel processors use little-endian order for data (least significant bytes at higher addresses), and some other processors use big-endian order (most significant bytes at higher addresses).

Example

// Reverse the bytes in a 32-bit integer, suitable for moving
// a LongWord between Intel and Sun, for example.
function Swap32(Value: LongWord): LongWord;
begin
  Result := Swap(Value shr 16) or (Swap(Value) shl 16); end; // If you really need to reverse the bytes in a 32-bit integer, // say to convert bit-endian to little-endian, don't use Swap // at all, but use the BSWAP instruction. function FastSwap(Value: LongWord): LongWord; register; overload; asm bswap eax end; // To swap an Int64 value, the argument is passed on the stack, // but the return value is in EAX:EDX. function FastSwap(Value: ...