Re: [dev] dwm bit fields conversion

From: pancake <pancake_AT_youterm.com>
Date: Mon, 15 Jul 2013 08:40:28 +0200

I should check generated code, but usually a mov is faster than mov+and+mov for setting a bit.

On Jul 14, 2013, at 23:22, Markus Teich <markus.teich_AT_stusta.mhn.de> wrote:

> Since this is just uncommon syntax (at least I haven't seen it before) and it is just used in the declaration I would be ok with it, if an additional comment explains it. It's not a strong opinion though, just an idea.
>
> --Markus
>
>
> Am 2013-07-14 21:32, schrieb Anselm R Garbe:
>> On 7 July 2013 16:49, koneu <koneu93_AT_googlemail.com> wrote:
>>> In Xdefs.h, Bool is typedef'd as int (= at least 2 bytes, sometimes more, depending on the implementation), of which we set the last bit to 1 or 0.
>>> In the Monitor and Client structures dwm uses, we can instead use char bit fields, storing up to 8 Bool values in 1 byte.
>>> diff --git a/dwm.c b/dwm.c
>>> index 314adf4..83af1f6 100644
>>> --- a/dwm.c
>>> +++ b/dwm.c
>>> _AT_@ -91,7 +91,7 @@ struct Client {
>>> int basew, baseh, incw, inch, maxw, maxh, minw, minh;
>>> int bw, oldbw;
>>> unsigned int tags;
>>> - Bool isfixed, isfloating, isurgent, neverfocus, oldstate, isfullscreen;
>>> + unsigned char isfixed :1, isfloating :1, isurgent :1, neverfocus :1, oldstate :1, isfullscreen :1, :2;
>>> Client *next;
>>> Client *snext;
>>> Monitor *mon;
>>> _AT_@ -121,8 +121,7 @@ struct Monitor {
>>> unsigned int seltags;
>>> unsigned int sellt;
>>> unsigned int tagset[2];
>>> - Bool showbar;
>>> - Bool topbar;
>>> + unsigned char showbar :1, topbar :1, :6;
>>> Client *clients;
>>> Client *sel;
>>> Client *stack;
>> I find this less readable than the usage of Bool. If memory
>> consumption would be a major dwm concern, I'd agree with such a
>> suggestion. But there are more important problems to focus on in dwm
>> 6.1 (fixed xinerama support).
>> Best regards,
>> Anselm
>
Received on Mon Jul 15 2013 - 08:40:28 CEST