Re: Tiny optimizations of bit testing operations

[Rein Klazes]

On Wed, 20 Oct 2004 19:48:05 +0900, you wrote:
> Hello,
>
> Changelog:
>     Dmitry Timoshkov 
>     Tiny optimizations of bit testing operations.

Testing with gcc 3.3.5:
> -
>        BOOL min_or_max_box = (wndPtr->dwStyle & WS_MAXIMIZEBOX) ||
> -
>                              (wndPtr->dwStyle & WS_MINIMIZEBOX);
> -
>        BOOL min_or_max_box = wndPtr->dwStyle & (WS_MAXIMIZEBOX | WS_MINIMIZEBOX);

At moderate optimization levels (-O1) gcc compiles this to identical
code.
> -
>    if((wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR) != 0)
> -
>    if (wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR)

At any optimization level, gcc compiles this to identical code.
>          if ((wndPtr->dwStyle & WS_VSCROLL) &&
> -
>            ((((wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR) != 0) && (ptClient.x <= rcClient.left + GetSystemMetrics(SM_CXVSCROLL))) ||
> -
>            (((wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR) == 0) && (ptClient.x >= rcClient.right - GetSystemMetrics(SM_CXVSCROLL)))))
> -
>            (((wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR) && (ptClient.x <= rcClient.left + GetSystemMetrics(SM_CXVSCROLL))) ||
> -
>            (!(wndPtr->dwExStyle & WS_EX_LEFTSCROLLBAR) && (ptClient.x >= rcClient.right - GetSystemMetrics(SM_CXVSCROLL)))))

Not different then the previous example.
> From the C point of view these bit logics are identical. The compiler

finds that out easy.

Rein.