Da finde ich gerade bei Stackoverflow Folgendes:
Delphi-Quellcode:
function ByteSwap64(Value: Int64): Int64;
asm
{$IF Defined(CPUX86)}
mov edx, [ebp+$08]
mov eax, [ebp+$0c]
bswap edx
bswap eax
{$ELSEIF Defined(CPUX64)}
mov rax, rcx
bswap rax
{$ELSE}
{$Message Fatal 'ByteSwap64 has not been implemented for this architecture.'}
{$ENDIF}
end;
von unserem Freund David Heffernan.
Tatsächlich "rax".