linux-kernel - Re: [PATCH v2 1/3] kernel: Provide a _

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Date:   Tue, 7 May 2019 14:06:54 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Jean Delvare <jdelvare@...e.com>,
        linux-arm-kernel@...ts.infradead.org,
        "open list:HARDWARE MONITORING" <linux-hwmon@...r.kernel.org>,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH v2 1/3] kernel: Provide a __pow10() function

On Tue, May 07, 2019 at 12:35:02PM -0700, Florian Fainelli wrote:
> Provide a simple macro that can return the value of 10 raised to a
> positive integer. We are going to use this in order to scale units from
> firmware to HWMON.
> 
> Signed-off-by: Florian Fainelli <f.fainelli@...il.com>
> ---
>  include/linux/kernel.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/include/linux/kernel.h b/include/linux/kernel.h
> index 2d14e21c16c0..62fc8bd84bc9 100644
> --- a/include/linux/kernel.h
> +++ b/include/linux/kernel.h
> @@ -294,6 +294,17 @@ static inline u32 reciprocal_scale(u32 val, u32 ep_ro)
>  	return (u32)(((u64) val * ep_ro) >> 32);
>  }
>  
> +/* Return in f the value of 10 raise to the power x */
> +#define __pow10(x, f)(					\
> +{							\
> +	typeof(x) __x = abs(x);				\
> +	f = 1;						\
> +	while (__x--)					\
> +		f *= 10;				\
> +	f;						\
> +}							\
> +)

Kind of unusual. I would have expected to use this like
	f = __pow10(x);
ie without having to provide f as parameter. That would be much less
confusing. I assume this is to make the result type independent, but
I am not sure if that is worth the trouble.

Are there users outside the hwmon code ? If not, it might be simpler
to keep it there for now.

Thanks,
Guenter

> +
>  #if defined(CONFIG_MMU) && \
>  	(defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP))
>  #define might_fault() __might_fault(__FILE__, __LINE__)
> -- 
> 2.17.1
>