linux-kernel - RE: [PATCH] ext4: simplify 32bit calculation of lblk

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Message-ID: <d04ead6617314074b297c10458010d6b@AcuMS.aculab.com>
Date:   Wed, 5 Apr 2023 11:43:47 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'chi wu' <wuchi.zero@...il.com>,
        Christoph Hellwig <hch@...radead.org>
CC:     "tytso@....edu" <tytso@....edu>,
        "adilger.kernel@...ger.ca" <adilger.kernel@...ger.ca>,
        "ojaswin@...ux.ibm.com" <ojaswin@...ux.ibm.com>,
        "ritesh.list@...il.com" <ritesh.list@...il.com>,
        "linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] ext4: simplify 32bit calculation of lblk

From: chi wu
> Sent: 05 April 2023 09:48
> 
> Christoph Hellwig <hch@...radead.org> 于2023年4月5日周三 13:40写道：
> >
> > On Mon, Apr 03, 2023 at 09:53:04PM +0800, wuchi wrote:
> > > -                     if (block > ext_block)
> > > -                             return ext_pblk + (block - ext_block);
> > > -                     else
> > > -                             return ext_pblk - (ext_block - block);
> > > +                     return ext_pblk + ((signed long long)block - (signed long long)ext_block);
> >
> > And what exactly is the value add here, except for turning an easy
> > to parse statement into a complex expression using casts?
> >
> Yes，it will be more complex. the original intention is to reduce the
> conditional branch.

What is wrong with just:
	return ext_pblk + block - ext_block;
(64bit + 32bit - 32bit)

	David

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