I have this procedure that swaps the bytes (low/high) of a Word variable (It does the same stuff as System.Swap function). The procedure works when the compiler optimization is OFF but not when it is ON. Can anybody help me with this?
procedure SwapWord(VAR TwoBytes: word);
asm
Mov EBX, TwoBytes
Mov AX, [EBX]
XCHG AL,AH
Mov [EBX], AX
end;
Fastest:
function ReverseWord(w: word): word;
asm
{$IFDEF CPUX64}
mov rax, rcx
{$ENDIF}
xchg al, ah
end;
In case you want to reverse DWORD too:
function ReverseDWord(dw: cardinal): cardinal;
asm
{$IFDEF CPUX64}
mov rax, rcx
{$ENDIF}
bswap eax
end;