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Subject: Re: [PATCH v8 5/8] Loongson: YeeLoong: add hardware monitoring
 driver
From:   Wu Zhangjin <wuzhangjin@gmail.com>
Reply-To: wuzhangjin@gmail.com
To:     Pavel Machek <pavel@ucw.cz>
Cc:     Ralf Baechle <ralf@linux-mips.org>, akpm@linux-foundation.org,
        linux-mips@linux-mips.org, linux-kernel@vger.kernel.org,
        Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        "Rafael J . Wysocki" <rjw@sisk.pl>, zhangfx@lemote.com,
        linux-laptop@vger.kernel.org,
        Stephen Rothwell <sfr@canb.auug.org.au>
In-Reply-To: <20091206084717.GD2766@ucw.cz>
References: <cover.1260082252.git.wuzhangjin@gmail.com>
         <d8789fa7e97d8a170c4e2516d7ef2d2fbbe42cc6.1260082252.git.wuzhangjin@gmail.com>
         <20091206084717.GD2766@ucw.cz>
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Organization: DSLab, Lanzhou University, China
Date:   Mon, 07 Dec 2009 08:54:58 +0800
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On Sun, 2009-12-06 at 09:47 +0100, Pavel Machek wrote: 
> Hi!
> 
> > +static int get_battery_current(void)
> > +{
> > +	s16 value;
> > +
> > +	value = (ec_read(REG_BAT_CURRENT_HIGH) << 8) |
> > +		(ec_read(REG_BAT_CURRENT_LOW));
> > +
> > +	if (value < 0)
> > +		value = ~value + 1;
> > +
> > +	return value;
> > +}
> 
> What is going on here? I thought the value is already in two's
> complement... Is the above equivalent of
> 
> 	      if (value < 0)
> 	      	 value = -value; 
> 
> ? If so, why? If not, can you add a comment?

Right, then, will use this instead:

static int get_battery_current(void)
{ 
	s16 value;

	value = (ec_read(REG_BAT_CURRENT_HIGH) << 8) |
		(ec_read(REG_BAT_CURRENT_LOW));

	return abs(value);
}

Thanks & Best Regards,
	Wu Zhangjin