Subject: Re: htonll, ntohll

From: Ramsay Jones <[email-masked]>
Date: Tue, 05 Nov 2013 00:00:24 +0000

On 31/10/13 13:24, Torsten Bögershausen wrote:
> On 2013-10-30 22.07, Ramsay Jones wrote:
[ ... ]
>> Yep, this was the first thing I did as well! ;-) (*late* last night)
>>
>> I haven't had time today to look into fixing up the msvc build
>> (or a complete re-write), so I look forward to seeing your solution.
>> (do you have msvc available? - or do you want me to look at fixing
>> it? maybe in a day or two?)
>>
> Ramsay,
> I don't have msvc, so feel free to go ahead, as much as you can.
> 
> I'll send a patch for the test code I have made, and put bswap.h on hold for a week
> (to be able to continue with t5601/connect.c)

Unfortunately, I haven't had much time to look into this.

I do have a patch (given below) that works on Linux, cygwin,
MinGW and msvc. However, the msvc build is still broken (as a
result of _other_ commits in this 'jk/pack-bitmap' branch; as
well as the use of a VLA in another commit).

So, I still have work to do! :(

Anyway, I thought I would send what I have, so you can take a look.
Note, that I don't have an big-endian machine to test this on, so
YMMV. Indeed, the *only* testing I have done is to run the test added
by this branch (t5310-pack-bitmaps.sh), which works on Linux, cygwin
and MinGW.

[Note: I have never particularly liked htons, htonl et.al., so adding
these htonll/ntohll functions doesn't thrill me! :-D For example see
this post[1], which echo's my sentiments exactly.]

HTH

ATB,
Ramsay Jones

[1] http://commandcenter.blogspot.co.uk/2012/04/byte-order-fallacy.html

-- >8 --
Subject: [PATCH] compat/bswap.h: Fix build on cygwin, MinGW and msvc

---
 compat/bswap.h | 97 ++++++++++++++++++++++++++++++++++++++++------------------
 1 file changed, 68 insertions(+), 29 deletions(-)

diff --git a/compat/bswap.h b/compat/bswap.h
index ea1a9ed..c18a78e 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -17,7 +17,20 @@ static inline uint32_t default_swab32(uint32_t val)
 		((val & 0x000000ff) << 24));
 }
 
+static inline uint64_t default_bswap64(uint64_t val)
+{
+	return (((val & (uint64_t)0x00000000000000ffULL) << 56) |
+		((val & (uint64_t)0x000000000000ff00ULL) << 40) |
+		((val & (uint64_t)0x0000000000ff0000ULL) << 24) |
+		((val & (uint64_t)0x00000000ff000000ULL) <<  8) |
+		((val & (uint64_t)0x000000ff00000000ULL) >>  8) |
+		((val & (uint64_t)0x0000ff0000000000ULL) >> 24) |
+		((val & (uint64_t)0x00ff000000000000ULL) >> 40) |
+		((val & (uint64_t)0xff00000000000000ULL) >> 56));
+}
+
 #undef bswap32
+#undef bswap64
 
 #if defined(__GNUC__) && (defined(__i386__) || defined(__x86_64__))
 
@@ -32,54 +45,80 @@ static inline uint32_t git_bswap32(uint32_t x)
 	return result;
 }
 
+#define bswap64 git_bswap64
+#if defined(__x86_64__)
+static inline uint64_t git_bswap64(uint64_t x)
+{
+	uint64_t result;
+	if (__builtin_constant_p(x))
+		result = default_bswap64(x);
+	else
+		__asm__("bswap %q0" : "=r" (result) : "0" (x));
+	return result;
+}
+#else
+static inline uint64_t git_bswap64(uint64_t x)
+{
+	union { uint64_t i64; uint32_t i32[2]; } tmp, result;
+	if (__builtin_constant_p(x))
+		result.i64 = default_bswap64(x);
+	else {
+		tmp.i64 = x;
+		result.i32[0] = git_bswap32(tmp.i32[1]);
+		result.i32[1] = git_bswap32(tmp.i32[0]);
+	}
+	return result.i64;
+}
+#endif
+
 #elif defined(_MSC_VER) && (defined(_M_IX86) || defined(_M_X64))
 
 #include <stdlib.h>
 
 #define bswap32(x) _byteswap_ulong(x)
+#define bswap64(x) _byteswap_uint64(x)
 
 #endif
 
-#ifdef bswap32
+#if defined(bswap32)
 
 #undef ntohl
 #undef htonl
 #define ntohl(x) bswap32(x)
 #define htonl(x) bswap32(x)
 
-#ifndef __BYTE_ORDER
-#	if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
-#		define __BYTE_ORDER BYTE_ORDER
-#		define __LITTLE_ENDIAN LITTLE_ENDIAN
-#		define __BIG_ENDIAN BIG_ENDIAN
-#	else
-#		error "Cannot determine endianness"
-#	endif
+#endif
+
+#if defined(bswap64)
+
+#undef ntohll
+#undef htonll
+#define ntohll(x) bswap64(x)
+#define htonll(x) bswap64(x)
+
+#else
+
+#undef ntohll
+#undef htonll
+
+#if !defined(__BYTE_ORDER)
+# if defined(BYTE_ORDER) && defined(LITTLE_ENDIAN) && defined(BIG_ENDIAN)
+#  define __BYTE_ORDER BYTE_ORDER
+#  define __LITTLE_ENDIAN LITTLE_ENDIAN
+#  define __BIG_ENDIAN BIG_ENDIAN
+# endif
+#endif
+
+#if !defined(__BYTE_ORDER)
+# error "Cannot determine endianness"
 #endif
 
 #if __BYTE_ORDER == __BIG_ENDIAN
 # define ntohll(n) (n)
 # define htonll(n) (n)
-#elif __BYTE_ORDER == __LITTLE_ENDIAN
-#	if defined(__GNUC__) && defined(__GLIBC__)
-#		include <byteswap.h>
-#	else /* GNUC & GLIBC */
-static inline uint64_t bswap_64(uint64_t val)
-{
-	return ((val & (uint64_t)0x00000000000000ffULL) << 56)
-		| ((val & (uint64_t)0x000000000000ff00ULL) << 40)
-		| ((val & (uint64_t)0x0000000000ff0000ULL) << 24)
-		| ((val & (uint64_t)0x00000000ff000000ULL) <<  8)
-		| ((val & (uint64_t)0x000000ff00000000ULL) >>  8)
-		| ((val & (uint64_t)0x0000ff0000000000ULL) >> 24)
-		| ((val & (uint64_t)0x00ff000000000000ULL) >> 40)
-		| ((val & (uint64_t)0xff00000000000000ULL) >> 56);
-}
-#	endif /* GNUC & GLIBC */
-#	define ntohll(n) bswap_64(n)
-#	define htonll(n) bswap_64(n)
-#else /* __BYTE_ORDER */
-#	error "Can't define htonll or ntohll!"
+#else
+# define ntohll(n) default_bswap64(n)
+# define htonll(n) default_bswap64(n)
 #endif
 
 #endif
-- 
1.8.4