Re: [PATCH] block-sha1: Windows declares ntohl() in winsock2.h

[Junio C Hamano <gitster@pobox.com>]

Sebastian Schuberth <sschuberth@gmail.com> writes:

> On Tue, Aug 18, 2009 at 18:08, Linus
> Torvalds<torvalds@linux-foundation.org> wrote:
>
>>> I'd suggest not using a gcc builtin, since if you're using gcc you might
>>> as well just use inline asm that has been around forever (unlike the
>>> builtin).
>>
>> That seems to be what glibc does too.
>>
>> Here's a patch.
>
> Looks good to me, compiles & runs fine on Windows (with Hannes' patch
> also applied).

But the Windows part that avoids arpa/inet.h and includes winsock2.h, only
to undef the two macros immediately after doing so, now looks quite silly.
Are there non i386/amd64 Windows we care about?

Squashing Linus's and Hannes's patch here is what I came up with.

-- >8 --
block-sha1: 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 minimally we need to include <winsock2.h> instead.
Sebastian Schuberth points out that they are implemented as out-of-line
functions on Windows, which defeats the use of these byteorder "macros"
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>,
---
diff --git a/block-sha1/sha1.c b/block-sha1/sha1.c
index a1228cf..fa909a3 100644
--- a/block-sha1/sha1.c
+++ b/block-sha1/sha1.c
@@ -7,8 +7,6 @@
  */
 
 #include <string.h>
-#include <arpa/inet.h>
-
 #include "sha1.h"
 
 #if defined(__i386__) || defined(__x86_64__)
@@ -24,8 +22,15 @@
 #define SHA_ROL(x,n)	SHA_ASM("rol", x, n)
 #define SHA_ROR(x,n)	SHA_ASM("ror", x, n)
 
+#undef htonl
+#undef ntohl
+#define htonl(x) ({ unsigned int __res; __asm__("bswap %0":"=r" (__res):"0" (x)); __res; })
+#define ntohl(x) htonl(x)
+
 #else
 
+#include <arpa/inet.h>
+
 #define SHA_ROT(X,l,r)	(((X) << (l)) | ((X) >> (r)))
 #define SHA_ROL(X,n)	SHA_ROT(X,n,32-(n))
 #define SHA_ROR(X,n)	SHA_ROT(X,32-(n),n)