From: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
To: Alexander Kuleshov <kuleshovmail@gmail.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH] fs/fat: calculate checksum in a loop instead of directly calculating
Date: Thu, 19 Feb 2015 04:25:54 +0900 [thread overview]
Message-ID: <878ufvowcd.fsf@mail.parknet.co.jp> (raw)
In-Reply-To: <1424285300-14431-1-git-send-email-kuleshovmail@gmail.com> (Alexander Kuleshov's message of "Thu, 19 Feb 2015 00:48:20 +0600")
Alexander Kuleshov <kuleshovmail@gmail.com> writes:
> static inline unsigned char fat_checksum(const __u8 *name)
> {
> + u8 i;
> unsigned char s = name[0];
> - s = (s<<7) + (s>>1) + name[1]; s = (s<<7) + (s>>1) + name[2];
> - s = (s<<7) + (s>>1) + name[3]; s = (s<<7) + (s>>1) + name[4];
> - s = (s<<7) + (s>>1) + name[5]; s = (s<<7) + (s>>1) + name[6];
> - s = (s<<7) + (s>>1) + name[7]; s = (s<<7) + (s>>1) + name[8];
> - s = (s<<7) + (s>>1) + name[9]; s = (s<<7) + (s>>1) + name[10];
> +
> + for (i = 1; i < 11; i++)
> + s = (s << 7) + (s >> 1) + name[i];
> +
> return s;
> }
When I wrote this, IIRC, there was measurable performance
difference. All major gcc versions are enough smart now to optimize this?
--
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
next prev parent reply other threads:[~2015-02-18 19:25 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-02-18 18:48 [PATCH] fs/fat: calculate checksum in a loop instead of directly calculating Alexander Kuleshov
2015-02-18 19:25 ` OGAWA Hirofumi [this message]
2015-02-18 19:46 ` Alexander Kuleshov
2015-02-18 20:32 ` OGAWA Hirofumi
2015-02-23 20:40 ` Heinrich Schuchardt
2015-02-24 2:42 ` OGAWA Hirofumi
2015-02-24 19:22 ` Heinrich Schuchardt
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