Can someone with assembler experience tell me what the pascal equivalent of the StdWndProc function is?

Can someone with assembler experience tell me what the pascal equivalent of the StdWndProc function is?

function StdWndProc(Window: HWND; Message, WParam: Longint;
  LParam: Longint): Longint; stdcall; assembler;
asm
        XOR     EAX,EAX
        PUSH    EAX
        PUSH    LParam
        PUSH    WParam
        PUSH    Message
        MOV     EDX,ESP
        MOV     EAX,[ECX].Longint[4]
        CALL    [ECX].Pointer
        ADD     ESP,12
        POP     EAX
end;

I understand it's purpose is to route windows messages to their destination window but I'd like to understand how it does this.