linux-kernel - Re: [RFC][PATCH] introduce ptr

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Message-ID: <yw1xaaoi8tjx.fsf@unicorn.mansr.com>
Date:	Thu, 19 Aug 2010 17:18:42 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] introduce ptr_diff()

David Howells <dhowells@...hat.com> writes:

> Namhyung Kim <namhyung@...il.com> wrote:
>
>> +	if (is_power_of_2(__size))				\
>> +		__diff = (__addr1 - __addr2) >> ilog2(__size);	\
>> +	else							\
>> +		__diff = (__addr1 - __addr2) / __size;		\
>
> You shouldn't need to do this.  The compiler's optimiser should switch a
> divide to a shift for a power-of-2 divisor.

Only when the numerator is provably non-negative, which is certainly
not the case here.

-- 
Måns Rullgård
mans@...sr.com

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