From: "H. Peter Anvin" <hpa@zytor.com>
To: Peter Zijlstra <peterz@infradead.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Cc: jsrhbz@kanargh.force9.co.uk,
christoph.muellner@theobroma-systems.com, linux@roeck-us.net,
linux@rasmusvillemoes.dk, paulmck@linux.vnet.ibm.com,
tglx@linutronix.de, mingo@kernel.org, akpm@linux-foundation.org,
maxime.coquelin@st.com, linux-kernel@vger.kernel.org,
martink@posteo.de, tytso@mit.edu,
linux-tip-commits@vger.kernel.org
Subject: Re: [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions
Date: Wed, 21 Jan 2015 12:22:19 -0800 [thread overview]
Message-ID: <54C00A7B.1000808@zytor.com> (raw)
In-Reply-To: <20150119100439.GN25256@twins.programming.kicks-ass.net>
On 01/19/2015 02:04 AM, Peter Zijlstra wrote:
> On Mon, Jan 19, 2015 at 07:54:22AM +1200, Linus Torvalds wrote:
>> Why?
>>
>> The 8- and 16- bit versions are the same as the 32-bit one. This seems
>> pointless. If you want something where the sign is in bit 3, they all
>> return the same value, just the return type differs, but that's really a
>> *caller* thing, no?
>
> Even for the 8bit ones? Since we have the *H and *L register we have
> more 8 bit regs than we have 16/32 bit regs and it might just be worth
> it.
Fewer, actually. gcc doesn't really use the H registers much, and
instead considers 8-bit values to occupy the whole register, but that
means only four are available in 32-bit mode.
-hpa
next prev parent reply other threads:[~2015-01-21 20:23 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-12 17:22 [PATCH v2] bitops.h: add sign_extend8(), 16 and 64 functions Martin Kepplinger
2015-01-12 17:28 ` [RFC] input: gtco: use bitops' sign_extend8 Martin Kepplinger
2015-01-12 17:28 ` [RFC] rtc: use sign_extend8 instead of manual conversion Martin Kepplinger
2015-01-12 17:28 ` [RFC] media: stb0899: use sign_extend8 instead of manual work Martin Kepplinger
2015-01-12 17:28 ` [RFC] hwmon: jc42: use bitops' sign_extend16 Martin Kepplinger
2015-01-12 19:53 ` Guenter Roeck
2015-01-12 19:48 ` [PATCH v2] bitops.h: add sign_extend8(), 16 and 64 functions Guenter Roeck
2015-01-14 16:56 ` [RFC PATCH 0/4] Example changes using proposed sign_extend functions Martin Kepplinger
2015-01-14 16:56 ` [PATCH 1/4] input: gtco: use bitops' sign_extend8 Martin Kepplinger
2015-01-14 16:56 ` [PATCH 2/4] rtc: use sign_extend8 instead of manual conversion Martin Kepplinger
2015-01-14 16:56 ` [PATCH 3/4] media: stb0899: use sign_extend8 instead of manual work Martin Kepplinger
2015-01-14 16:56 ` [PATCH 4/4] hwmon: jc42: use bitops' sign_extend16 Martin Kepplinger
2015-01-18 19:06 ` [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions tip-bot for Martin Kepplinger
[not found] ` <CA+55aFyc7TbnLBi3rcQDrtkwg9TgDnb5dAfupMGSbTKZC6Xd0g@mail.gmail.com>
2015-01-19 1:11 ` Guenter Roeck
2015-01-19 4:00 ` Linus Torvalds
2015-01-20 12:30 ` [PATCH v3 0/2] bitops.h: add sign_extend64() API and improve doc Martin Kepplinger
2015-01-20 12:30 ` [PATCH 1/2] bitops.h: improve documentation for sign_extend32() Martin Kepplinger
2015-01-20 12:30 ` [PATCH 2/2] bitops.h: Add sign_extend64() API Martin Kepplinger
2015-01-19 10:04 ` [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions Peter Zijlstra
2015-01-21 20:22 ` H. Peter Anvin [this message]
2015-02-05 7:17 ` Ingo Molnar
2015-02-05 14:11 ` Guenter Roeck
2015-02-12 11:11 ` Example use of sign_extend64() Martin Kepplinger
2015-02-12 11:11 ` [RFC][PATCH] arch: sh: use sign_extend64() for sign extension Martin Kepplinger
2015-02-05 16:39 ` [tip:core/types] bitops: Add sign_extend8(), 16 and 64 functions H. Peter Anvin
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