From mboxrd@z Thu Jan  1 00:00:00 1970
From: Graeme Russ <graeme.russ@gmail.com>
Date: Wed, 15 Jun 2011 22:42:55 +1000
Subject: [U-Boot] [PATCH v3 02/10] armv7: add miscellaneous
	utility	macros
In-Reply-To: <20110615120447.9EEC4655C6@gemini.denx.de>
References: <1299589658-30896-1-git-send-email-aneesh@ti.com>	<1305202276-27784-3-git-send-email-aneesh@ti.com>	<20110515184421.D7AB91491B06@gemini.denx.de>	<4DD13DA3.3030505@ti.com>
	<4DECF8DA.9030806@ti.com>	<20110606185046.BB8991736815@gemini.denx.de>	<4DEDE8D9.7030306@ti.com>	<20110607103923.7E1CC1B993A8@gemini.denx.de>	<4DEE161B.2050402@ti.com>	<20110607154028.D6540195494F@gemini.denx.de>	<4DEF62A6.7060706@ti.com>	<20110608214124.849821B993A8@gemini.denx.de>	<4DF71FBF.6030408@ti.com>	<20110614105115.01D6611EEDAF@gemini.denx.de>	<4DF7488A.6000909@ti.com>	<20110614135335.A750811EEDAF@gemini.denx.de>	<4DF871E3.8080307@ti.com>	<20110615092014.F080219E5AC1@gemini.denx.de>	<4DF89102.9040508@ti.com>
	<20110615120447.9EEC4655C6@gemini.denx.de>
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On 15/06/11 22:04, Wolfgang Denk wrote:
> Dear Aneesh V,
> 
> In message <4DF89102.9040508@ti.com> you wrote:
>>
>> Will you accept something like this?
>>
>> a_val = (reg & a_mask) >> a_shift;
> 
> Yes, of course (that's what seems most natural to me).
> 

Me too - The code is obvious - the desired value is being masked out of a
larger composite value and then shifted right to bit 0

And to set the value then you have:

	reg &= ~a_mask;				/* Clear a_val */
	reg |= (a_val << a_shift) & a_mask;	/* Set new a_val */

AND'ing with a_mask is required to prevent accidental clobbering when a_val
is out-of-range. May give undesirable results by setting an illegal a_val,
but@least you don't clobber unrelated bit fields

Regards,

Graeme