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Date: Thu, 16 Jul 2015 11:19:22 +0200
From: Lars-Peter Clausen <lars@metafoo.de>
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To: Gwendal Grignou <gwendal@chromium.org>
CC: linux-iio@vger.kernel.org
Subject: Re: Question about IIO_DEGREE_TO_RAD macro in include/linux/iio.h
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On 07/16/2015 01:24 AM, Gwendal Grignou wrote:
> Lars,
>
> Looking at the macro IIO_DEGREE_TO_RAD() to translate degree/s into rad/s,
> I don't understand why we add an offset when doing the conversion:
>
> #define IIO_DEGREE_TO_RAD(deg) (((deg) * 314159ULL + 9000000ULL) /
> 18000000ULL)
>
> Shouldn't it just be
> #define IIO_DEGREE_TO_RAD(deg) (((deg) * 314159ULL) / 18000000ULL)

Hi,

The offset is for rounding to the nearest integer. Without the offset it 
would round down.

- Lars