From: Artur Skawina <art.08.09@gmail•com>
To: Sebastian Schuberth <sschuberth@gmail•com>
Cc: Johannes Sixt <j.sixt@viscovery•net>,
msysGit <msysgit@googlegroups•com>,
Junio C Hamano <gitster@pobox•com>,
Git Mailing List <git@vger•kernel.org>
Subject: Re: [PATCH] block-sha1: Windows declares ntohl() in winsock2.h
Date: Tue, 18 Aug 2009 14:56:49 +0200 [thread overview]
Message-ID: <4A8AA511.1060205@gmail.com> (raw)
In-Reply-To: <4A8A8661.5060908@gmail.com>
Sebastian Schuberth wrote:
> As ntohl()/htonl() are function calls (that internally do shifts), I
> doubt they're faster than the shift macros, though I haven't measured
> it. However, I do not suggest to go for the macros on Windows/Intel, but
> to apply the following patch on top of your patch:
> On Windows/Intel, ntohl()/htonl() are function calls that do shifts to
> swap the
> byte order. Using the native bswap instruction boths gets rid of the
> shifts and
> the function call overhead to gain some performance.
Umm, nothing like this should be needed on linux; the compiler/glibc
will choose bswap itself. (see endian.h and bits/byteswap.h).
I did try using __builtin_bswap32 directly and the result was a few
(3 or 4, iirc) differently scheduled instructions, that's all, no
performance difference.
> * Performance might be improved if the CPU architecture is OK with
> - * unaligned 32-bit loads and a fast ntohl() is available.
> + * unaligned 32-bit loads and a fast ntohl() is available. On Intel,
> + * use the bswap built-in to get rid of the function call overhead.
> * Otherwise fall back to byte loads and shifts which is portable,
> * and is faster on architectures with memory alignment issues.
> */
>
> -#if defined(__i386__) || defined(__x86_64__) || \
> - defined(__ppc__) || defined(__ppc64__) || \
> - defined(__powerpc__) || defined(__powerpc64__) || \
> - defined(__s390__) || defined(__s390x__)
> +#if defined(__i386__) || defined(__x86_64__)
>
> +#define get_be32(p) __builtin_bswap32(*(unsigned int *)(p))
> +#define put_be32(p, v) do { *(unsigned int *)(p) = __builtin_bswap32(v); } while (0)
> +
> +#elif defined(__ppc__) || defined(__ppc64__) || \
> + defined(__powerpc__) || defined(__powerpc64__) || \
> + defined(__s390__) || defined(__s390x__)
I'd limit it to windows and any other ia32 platform that doesn't pick the
bswaps itself; as is, it just adds an unnecessary hidden gcc dependency.
Hmm, it's actually a gcc-4.3+ dependency, so it won't even build w/ gcc 4.2;
something like this would be required: "(__GNUC__>=4 && __GNUC_MINOR__>=3)" .
artur
next prev parent reply other threads:[~2009-08-18 12:57 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-18 7:15 [PATCH] block-sha1: Windows declares ntohl() in winsock2.h Johannes Sixt
2009-08-18 10:45 ` Sebastian Schuberth
2009-08-18 11:07 ` Junio C Hamano
2009-08-18 11:28 ` Sebastian Schuberth
2009-08-18 12:56 ` Artur Skawina [this message]
2009-08-18 13:17 ` Sebastian Schuberth
2009-08-18 13:39 ` Junio C Hamano
2009-08-18 15:40 ` Linus Torvalds
2009-08-18 16:08 ` Linus Torvalds
2009-08-18 16:23 ` Sebastian Schuberth
2009-08-18 16:43 ` Junio C Hamano
2009-08-18 16:30 ` Nicolas Pitre
2009-08-18 16:43 ` Nicolas Pitre
2009-08-18 16:50 ` Junio C Hamano
2009-08-18 18:01 ` Nicolas Pitre
2009-08-18 19:00 ` Junio C Hamano
2009-08-18 19:22 ` Nicolas Pitre
2009-08-18 19:26 ` [PATCH] make sure byte swapping is optimal for git Nicolas Pitre
2009-08-18 19:37 ` [PATCH] block-sha1: guard gcc extensions with __GNUC__ Nicolas Pitre
2009-08-18 19:40 ` [PATCH] block-sha1: Windows declares ntohl() in winsock2.h Junio C Hamano
2009-08-18 19:56 ` Brandon Casey
2009-08-18 20:10 ` Nicolas Pitre
2009-08-18 20:25 ` Linus Torvalds
2009-08-18 20:29 ` Brandon Casey
2009-08-20 2:26 ` Nicolas Pitre
2009-08-20 2:30 ` Linus Torvalds
2009-08-20 2:45 ` Brandon Casey
2009-08-18 16:59 ` Sebastian Schuberth
2009-08-18 17:05 ` Junio C Hamano
2009-08-18 18:16 ` Nicolas Pitre
2009-08-18 20:17 ` Junio C Hamano
2009-08-18 20:30 ` Junio C Hamano
2009-08-18 20:49 ` Nicolas Pitre
2009-08-18 18:10 ` Nicolas Pitre
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