linux-kernel - Re: [PATCH v4] iio: chemical: Add support for Bosch BME680 sensor

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Message-ID: <20180721172924.53619e6a@archlinux>
Date:   Sat, 21 Jul 2018 17:29:24 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Himanshu Jha <himanshujha199640@...il.com>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Hartmut Knaack <knaack.h@....de>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Peter Meerwald <pmeerw@...erw.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Daniel Baluta <daniel.baluta@...il.com>
Subject: Re: [PATCH v4] iio: chemical: Add support for Bosch BME680 sensor

On Sat, 21 Jul 2018 21:22:30 +0530
Himanshu Jha <himanshujha199640@...il.com> wrote:

> On Sat, Jul 21, 2018 at 06:43:51PM +0300, Andy Shevchenko wrote:
> > On Sat, Jul 21, 2018 at 6:36 PM, Himanshu Jha
> > <himanshujha199640@...il.com> wrote:
> >   
> > >> > +   /* Look up table 1 for the possible gas range values */
> > >> > +   u32 lookupTable1[16] = {2147483647u, 2147483647u, 2147483647u,
> > >> > +                           2147483647u, 2147483647u, 2126008810u,
> > >> > +                           2147483647u, 2130303777u, 2147483647u,
> > >> > +                           2147483647u, 2143188679u, 2136746228u,
> > >> > +                           2147483647u, 2126008810u, 2147483647u,
> > >> > +                           2147483647u};  
> > 
> > This one needs perhaps a bit of though, but...
> >   
> > >> > +   /* Look up table 2 for the possible gas range values */
> > >> > +   u32 lookupTable2[16] = {4096000000u, 2048000000u, 1024000000u,
> > >> > +                           512000000u, 255744255u, 127110228u, 64000000u,
> > >> > +                           32258064u, 16016016u, 8000000u, 4000000u,
> > >> > +                           2000000u, 1000000u, 500000u, 250000u, 125000u};  
> > 
> > ...this one obviously just a not needed one. You may replace it with a
> > one constant and simple calculation to get either value (index from
> > value, or value from index).  
> 
> Not sure to understand your opinion!?
> 
> Anything related to increase to .ro segment ?
> 
> I think adding is better to let compiler optimise the code a bit
> further.

No, I missed this as didn't look too closely at those numbers.
They are almost by not quite simple power's of 2 * 125000.
Question is whether the very very small difference from that matter or not...

Andy is suggesting replacing this block of data with an equation that is
'near enough'.
> 
> > -- 
> > With Best Regards,
> > Andy Shevchenko  
>