Nicolas Pitre <nico@xxxxxxx> writes:
> 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@xxxxxxx>
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@xxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Nicolas Pitre <nico@xxxxxxx>
Signed-off-by: Junio C Hamano <gitster@xxxxxxxxx>
---
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
--
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