From: Segher Boessenkool <segher@kernel.crashing.org>
To: michael@ellerman.id.au
Cc: linuxppc-dev list <linuxppc-dev@ozlabs.org>,
Kumar Gala <kumar.gala@freescale.com>,
Jin Zhengxiong <Jason.Jin@freescale.com>
Subject: Re: [PATCH 1/3] MSI driver for Freescale 83xx/85xx/86xx cpu
Date: Wed, 23 Apr 2008 18:05:47 +0200 [thread overview]
Message-ID: <8c9045cf69926c5ea881b780054e1c17@kernel.crashing.org> (raw)
In-Reply-To: <1208929545.9212.12.camel@concordia.ozlabs.ibm.com>
>>> data = ((hwirq / 32) << 5) | ((hwirq % 32) & 0x1F)
>>>
>>> Which doesn't seem to actually do anything?
>>
>> It's not a no-op, because hwirq is signed. It probably should be
>> unsigned, like most things.
>
> You'll have to draw me a picture.
In C, signed division is round-towards-zero, while unsigned division
is round-towards-negative-infinity. Suppose hwirq is -1, then
hwirq/32 is 0 and hwirq%32 is -1, so that the full expression above
will be 0x1f, not -1. There is no such problem if hwirq would be
unsigned; the compiler can generate better code in that case.
Segher
prev parent reply other threads:[~2008-04-23 16:06 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-04-19 9:27 [PATCH 1/3] MSI driver for Freescale 83xx/85xx/86xx cpu Jason Jin
[not found] ` <1208597267-30960-2-git-send-email-Jason.jin@freescale.com>
2008-04-19 9:27 ` [PATCH 3/3] Enable MSI support for 85xxds board Jason Jin
2008-04-18 11:51 ` Segher Boessenkool
2008-04-21 6:21 ` [PATCH 1/3] MSI driver for Freescale 83xx/85xx/86xx cpu Michael Ellerman
2008-04-21 10:01 ` Jin Zhengxiong
2008-04-22 4:35 ` Michael Ellerman
2008-04-22 5:15 ` Jin Zhengxiong
2008-04-22 13:22 ` Segher Boessenkool
2008-04-23 5:45 ` Michael Ellerman
2008-04-23 16:05 ` Segher Boessenkool [this message]
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=8c9045cf69926c5ea881b780054e1c17@kernel.crashing.org \
--to=segher@kernel.crashing.org \
--cc=Jason.Jin@freescale.com \
--cc=kumar.gala@freescale.com \
--cc=linuxppc-dev@ozlabs.org \
--cc=michael@ellerman.id.au \
/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 a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).