Re: [PATCH] block-sha1: Windows declares ntohl() in winsock2.h
- From
Junio C Hamano <gitster@pobox.com>
- Date
- Aug 18, 2009, 20:17 UTC
- Message-ID
- <7vprasc1vu.fsf@alter.siamese.dyndns.org>
- In-Reply-To
- <alpine.LFD.2.00.0908181411320.6044@xanadu.home>
Nicolas Pitre <nico@cam.org> writes:
Show 9 quoted lines
> On Tue, 18 Aug 2009, Junio C Hamano wrote: > >> To reduce confusion, you may want to rename compat/bswap.h to something >> like compat/ntohl-htonl-fix.h ;-) > > Bah. If you wish, you can edit the patch directly for this, unless you > really prefer me to repost. Maybe we might want to add a 8-byte > versions of those as well eventually, which is why I chose a more > generic name.
Ok, here is what I came up with after many squashing...
-- >8 -- From: Nicolas Pitre <nico@cam.org> Date: Tue, 18 Aug 2009 12:43:08 -0400 Subject: [PATCH] bswap: avoid potentially inefficient ntohl/htonl on i386/x86-64
Johannes Sixt reports that on Windows ntohl()/htonl() are not found in <arpa/inet.h>, and as a minimal fix we need to include <winsock2.h> instead. Sebastian Schuberth points out that they are implemented as out-of-line functions on Windows, which defeats these byteorder "macros" used for performance.
Use bswap instruction through gcc inline asm instead on i386/x86-64 as a generic solution to this.
Signed-off-by: Johannes Sixt <j6t@kdbg.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Nicolas Pitre <nico@cam.org> Signed-off-by: Junio C Hamano <gitster@pobox.com> --- block-sha1/sha1.c | 4 +--- compat/bswap.h | 19 +++++++++++++++++++ git-compat-util.h | 2 ++ 3 files changed, 22 insertions(+), 3 deletions(-) create mode 100644 compat/bswap.h
diff --git a/block-sha1/sha1.c b/block-sha1/sha1.c index 464cb25..51a27c1 100644 --- a/block-sha1/sha1.c +++ b/block-sha1/sha1.c @@ -4,9 +4,7 @@ * and to avoid unnecessary copies into the context array. */ -#include <string.h> -#include <arpa/inet.h> - +#include "../git-compat-util.h" #include "sha1.h" #if defined(__i386__) || defined(__x86_64__) diff --git a/compat/bswap.h b/compat/bswap.h new file mode 100644 index 0000000..78fd2df --- /dev/null +++ b/compat/bswap.h @@ -0,0 +1,19 @@ +/* + * Let's make sure we always have a sane definition for ntohl()/htonl(). + * Some libraries define those as a function call, just to perform byte + * swapping, bringing significant overhead to what should be a simple + * operation. + */ + +#if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__)) + +#define bswap32(x) ({ \ + unsigned int __res; \ + __asm__("bswap %0" : "=r" (__res) : "0" (x)); \ + __res; }) +#undef ntohl +#undef htonl +#define ntohl(x) bswap32(x) +#define htonl(x) bswap32(x) + +#endif diff --git a/git-compat-util.h b/git-compat-util.h index 9f941e4..000859e 100644 --- a/git-compat-util.h +++ b/git-compat-util.h @@ -176,6 +176,8 @@ extern char *gitbasename(char *); #endif #endif +#include "compat/bswap.h" + /* General helper functions */ extern void usage(const char *err) NORETURN; extern void die(const char *err, ...) NORETURN __attribute__((format (printf, 1, 2)));
-- 1.6.4.245.g50659