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From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Junio C Hamano <gitster@pobox.com>
Cc: git@vger.kernel.org, Jeff King <peff@peff.net>,
	Michael Kebe <michael.kebe@gmail.com>,
	"Liam R . Howlett" <Liam.Howlett@Oracle.com>,
	Adam Dinwoodie <adam@dinwoodie.org>,
	Stefan Beller <sbeller@google.com>
Subject: Re: [PATCH 1/3] sha1dc: update from my PR #36
Date: Tue, 27 Jun 2017 21:35:09 +0200	[thread overview]
Message-ID: <87r2y5jkb6.fsf@gmail.com> (raw)
In-Reply-To: <xmqq7ezx1c31.fsf@gitster.mtv.corp.google.com>


On Tue, Jun 27 2017, Junio C. Hamano jotted:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> Because in the current code is, abbreviated:
>>
>>     #if (defined(_BYTE_ORDER) || defined(__BYTE_ORDER) || defined(__BYTE_ORDER__))
>>     #if /* byte order is bendian */
>>     #define SHA1DC_BIGENDIAN
>>     #endif
>>     #else
>>     #if /*some processor tests/* || defined(__sparc))
>>     #define SHA1DC_BIGENDIAN
>>     #endif
>>
>> And since Solaris defines _BYTE_ORDER we never get to checking __sparc,
>> and in fact the "/* byte order is bendian */" test errors out.
>>
>> This is fixed by my patch, where we first check gcc settings, then
>> glibc, then processors, and finally _BYTE_ORDER (but as discussed that
>> last bit could be adjusted to sun && _BYTE_ORDER, if we can find what
>> "sun" is.
>
> Well, if Solaris defines _BYTE_ORDER, doesn't that mean they define
> two constants _BIG_ENDIAN and _LITTLE_ENDIAN to compare it with?

No, under gcc/clang & glibc you're expected to compare them. Under
Solaris it's just defined(_BIG_ENDIAN), but as explained in another
comment this whole thing actually turns out to be not needed, on Solaris
it's sufficient that we fall through and check __sparc.

> that is the case, I suspect that the change to make "comparison
> between __BYTE_ORDER and __BIG_ENDIAN for GCC only" is going in a
> wrong direction, as it wants to take the same approach as GCC, but
> just uses a slightly different symbol.
>
> I wonder if the approach like the following might be cleaner to
> extend as we find other oddball platforms.
>
>     #undef __SHA1DC_BYTE_ORDER
>     #if defined(_BYTE_ORDER)
>     #define __SHA1DC_BYTE_ORDER _BYTE_ORDER
>     #elif defined(__BYTE_ORDER)
>     #define __SHA1DC_BYTE_ORDER __BYTE_ORDER
>     #elif defined(__BYTE_ORDER__))
>     #define __SHA1DC_BYTE_ORDER __BYTE_ORDER__
>     #endif
>
>     #ifdef __SHA1DC_BYTE_ORDER
>      #undef __SHA1DC_BIG_ENDIAN
>      /* do the same for variations of BIG_ENDIAN constant */
>      #if defined(_BIG_ENDIAN)
> 	...
>      #endif
>
>      #if __SHA1DC_BYTE_ORDER == __SHA1DC_BIG_ENDIAN
>      #define SHA1DC_BIGENDIAN
>      #endif

As explained above no, because some e.g. _BIG_ENDIAN don't have a value
at all.

But more generally we can't assume that we can just exhaustively search
for some ^_*BIG_ENDIAN_*$ macro and compare it with some
^_*BYTE_ORDER_*$ value and get an expected result.

>     #else
>      /*
>       * as the platform does not use "compare BYTE-ORDER with
>       * BIG_ENDIAN macro" strategy, defined-ness of BIG_ENDIAN
>       * may be usable as a sign that it is a big-endian box.
>       */
>     #endif

  parent reply	other threads:[~2017-06-27 19:35 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-06-26  7:32 Compile Error v2.13.2 on Solaris SPARC Michael Kebe
     [not found] ` <87lgofcf7r.fsf@gmail.com>
2017-06-26 12:36   ` Michael Kebe
2017-06-26 12:47     ` Ævar Arnfjörð Bjarmason
2017-06-26 14:00       ` Michael Kebe
2017-06-26 18:31         ` Ævar Arnfjörð Bjarmason
2017-06-26 18:29       ` Liam R. Howlett
     [not found] ` <87fuem7aw2.fsf@gmail.com>
2017-06-27  5:41   ` Michael Kebe
2017-06-27  6:28     ` Michael Kebe
2017-06-27 16:28       ` Liam R. Howlett
2017-06-27 17:38         ` Junio C Hamano
2017-06-27 18:29           ` Liam R. Howlett
2017-06-27 18:55             ` Ævar Arnfjörð Bjarmason
2017-06-27 17:59         ` Ævar Arnfjörð Bjarmason
2017-06-27 12:17 ` [PATCH 0/3] update sha1dc from PR #36 Ævar Arnfjörð Bjarmason
2017-06-27 18:37   ` Stefan Beller
2017-06-27 20:33   ` [PATCH v2 " Ævar Arnfjörð Bjarmason
2017-06-27 21:37     ` Junio C Hamano
2017-06-27 21:38     ` Junio C Hamano
2017-06-27 22:24       ` Ævar Arnfjörð Bjarmason
2017-06-28 21:42       ` Ævar Arnfjörð Bjarmason
2017-06-28 22:02         ` Junio C Hamano
2017-06-27 20:33   ` [PATCH v2 1/3] sha1dc: correct endian detection for Solaris (and others?) Ævar Arnfjörð Bjarmason
2017-06-27 20:33   ` [PATCH v2 2/3] sha1dc: optionally use sha1collisiondetection as a submodule Ævar Arnfjörð Bjarmason
2017-06-27 20:33   ` [PATCH v2 3/3] sha1collisiondetection: automatically enable when submodule is populated Ævar Arnfjörð Bjarmason
2017-07-01 22:05   ` [PATCH v3 0/3] Update sha1dc from upstream Ævar Arnfjörð Bjarmason
2017-07-01 22:05   ` [PATCH v3 1/3] sha1dc: update " Ævar Arnfjörð Bjarmason
2017-07-01 22:05   ` [PATCH v3 2/3] sha1dc: optionally use sha1collisiondetection as a submodule Ævar Arnfjörð Bjarmason
2017-07-03 17:11     ` Junio C Hamano
2017-07-03 20:29       ` Ævar Arnfjörð Bjarmason
2017-07-04 17:26         ` Junio C Hamano
2017-07-04 22:50           ` Ævar Arnfjörð Bjarmason
2017-07-05  0:36             ` Stefan Beller
2017-07-05  1:56               ` Junio C Hamano
2017-07-05 17:46                 ` Stefan Beller
2017-07-05 18:03                   ` Ævar Arnfjörð Bjarmason
2017-07-01 22:05   ` [PATCH v3 3/3] sha1collisiondetection: automatically enable when submodule is populated Ævar Arnfjörð Bjarmason
2017-06-27 12:17 ` [PATCH 1/3] sha1dc: update from my PR #36 Ævar Arnfjörð Bjarmason
2017-06-27 15:22   ` Junio C Hamano
2017-06-27 15:53     ` Junio C Hamano
2017-06-27 18:07       ` Ævar Arnfjörð Bjarmason
2017-06-27 15:55     ` Junio C Hamano
2017-06-27 16:31       ` Liam R. Howlett
2017-06-27 18:11       ` Ævar Arnfjörð Bjarmason
2017-06-27 19:10         ` Junio C Hamano
2017-06-27 19:33           ` Junio C Hamano
2017-06-27 19:35           ` Ævar Arnfjörð Bjarmason [this message]
2017-06-27 19:38             ` Junio C Hamano
2017-06-27 19:38           ` Liam R. Howlett
2017-06-27 19:48             ` Junio C Hamano
2017-06-27 18:06     ` Ævar Arnfjörð Bjarmason
2017-06-27 18:12       ` Junio C Hamano
2017-06-27 18:19         ` Ævar Arnfjörð Bjarmason
2017-06-27 20:17           ` Junio C Hamano
2017-06-27 18:23       ` Junio C Hamano
2017-06-27 18:52         ` Ævar Arnfjörð Bjarmason
2017-06-27 12:17 ` [PATCH 2/3] sha1dc: optionally use sha1collisiondetection as a submodule Ævar Arnfjörð Bjarmason
2017-06-27 18:46   ` Stefan Beller
2017-06-27 18:56     ` Ævar Arnfjörð Bjarmason
2017-06-27 12:17 ` [PATCH 3/3] sha1collisiondetection: automatically enable when submodule is populated Ævar Arnfjörð Bjarmason

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