linux-kernel - Re: [RFC V1] lib: cordic: add library module for cordic angle calculation

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Message-ID: <4DDE1DD0.4000404@broadcom.com>
Date:	Thu, 26 May 2011 11:30:56 +0200
From:	"Arend van Spriel" <arend@...adcom.com>
To:	"Larry Finger" <Larry.Finger@...inger.net>
cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
	"John W. Linville" <linville@...driver.com>,
	"Greg Kroah-Hartman" <gregkh@...e.de>,
	"Dan Carpenter" <error27@...il.com>
Subject: Re: [RFC V1] lib: cordic: add library module for cordic angle
 calculation

On 05/25/2011 10:35 PM, Larry Finger wrote:
> On 05/25/2011 02:40 PM, Arend van Spriel wrote:
>> The brcm80211 driver in the staging tree has a cordic function to
>> determine cosine and sine for a given angle. Feedback received from
>> John Linville suggested that these kind of functions should be made
>> available to others as a library function in the kernel tree.
> There is a similar routine in b43, thus this library function will likely have
> at least 2 users.

I know (forgot to mention it in the commit message). Henry Ptasinski 
(broadcom colleague) actually verified both functions against Matlab 
implementation (or Scilab, if you prefer open-source ;-) ). The b43 
version has a more limited range of the angle input in which the 
calculation is accurate.

>> +static const s32 AtanTbl[] = {
> In Documentation/CodingStyle, variables with mixed-case names are frownid upon.

No frowning needed. I will change it ;-)

>
>> +/*
>> + * cordic_calc_iq() - calculates the i/q coordinate for given angle
>> + *
>> + * theta: angle in degrees for which i/q coordinate is to be calculated
>> + * coord: function output parameter holding the i/q coordinate
>> + */
>> +void cordic_calc_iq(s32 theta, struct cordic_iq *coord)
> As "coord" is only for output, why not have this be a function returning a
> struct cordic_iq?

Only to avoid passing the structure over the stack. Given the fact that 
it is only 8 bytes (4 bytes extra) I think it is ok to change it.

Gr. AvS

-- 
Almost nobody dances sober, unless they happen to be insane.
-- H.P. Lovecraft --


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