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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=878ufvowcd.fsf@mail.parknet.co.jp \
--to=hirofumi@mail.parknet.co.jp \
--cc=kuleshovmail@gmail.com \
--cc=linux-kernel@vger.kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.