linux-kernel - Re: [PATCH 1/4] media: si2168: use bits instead of bool for flags

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Date:   Thu, 10 Oct 2019 12:55:44 +0200
From:   Gon Solo <gonsolo@...il.com>
To:     Mauro Carvalho Chehab <mchehab+samsung@...nel.org>
Cc:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...radead.org>,
        JP <jp@...w.nl>, crope@....fi, Sean Young <sean@...s.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] media: si2168: use bits instead of bool for flags

On Fri, Oct 04, 2019 at 10:15:22AM -0300, Mauro Carvalho Chehab wrote:
> Using bool on struct is not recommended, as it wastes lots of
> space. So, instead, let's use bits.

Wouldn't "bool b:1;" even be better? I performed a little test:

#include <stdbool.h>
#include <stdio.h>

struct uints {
	unsigned int a0;
	unsigned int a1;
	unsigned int a2;
	unsigned int a3;
	unsigned int a4;
	unsigned int a5;
	unsigned int a6;
	unsigned int a7;
};

struct bools {
	bool a0;
	bool a1;
	bool a2;
	bool a3;
	bool a4;
	bool a5;
	bool a6;
	bool a7;
};

struct bit_uints {
	unsigned int a0:1;
	unsigned int a1:1;
	unsigned int a2:1;
	unsigned int a3:1;
	unsigned int a4:1;
	unsigned int a5:1;
	unsigned int a6:1;
	unsigned int a7:1;
};

struct bit_bools {
	bool a0:1;
	bool a1:1;
	bool a2:1;
	bool a3:1;
	bool a4:1;
	bool a5:1;
	bool a6:1;
	bool a7:1;
};

int main() {
	printf("bit_uints: %ld\n", sizeof(struct bit_uints));
	printf("bit_bools: %ld\n", sizeof(struct bit_bools));
	printf("uints: %ld\n", sizeof(struct uints));
	printf("bools: %ld\n", sizeof(struct bools));
}

Result:

bit_uints: 4
bit_bools: 1
uints: 32
bools: 8

I know with different types within the struct it looks different, but
still.

g