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From: david@tethera.net
To: notmuch@notmuchmail.org
Subject: [PATCH v2] util: detect byte order
Date: Tue, 26 Nov 2013 20:38:14 -0400
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From: David Bremner <david@tethera.net>

Unfortunately old versions of GCC and clang do not provide byte order
macros, so we re-invent them.

If UTIL_BYTE_ORDER is not defined or defined to 0, we fall back to
macros supported by recent versions of GCC and clang
---

I think I got all of Tomi's comments, including the most serious one
about the test in endian-utils.h (LITTLE twice instead of BIG,
LITTLE).

 configure          | 24 ++++++++++++++++++++++--
 lib/libsha1.c      | 21 +++++++--------------
 util/endian-util.h | 38 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 67 insertions(+), 16 deletions(-)
 create mode 100644 util/endian-util.h

diff --git a/configure b/configure
index 1a8e939..a0c6771 100755
--- a/configure
+++ b/configure
@@ -441,6 +441,19 @@ else
 EOF
 fi
 
+printf "Checking byte order... "
+cat> _byteorder.c <<EOF
+#include <stdio.h>
+#include <stdint.h>
+uint32_t test = 0x34333231;
+int main() { printf("%.4s\n", (const char*)&test); return 0; }
+EOF
+${CC} ${CFLAGS} _byteorder.c -o _byteorder > /dev/null 2>&1
+util_byte_order=$(./_byteorder)
+echo $util_byte_order
+
+#rm -f _byteorder _byteorder.c
+
 if [ $errors -gt 0 ]; then
     cat <<EOF
 
@@ -702,6 +715,9 @@ prefix = ${PREFIX}
 # LIBDIR_IN_LDCONFIG value below is still set correctly.
 libdir = ${LIBDIR:=\$(prefix)/lib}
 
+# byte order within a 32 bit word. 1234 = little, 4321 = big, 0 = guess
+UTIL_BYTE_ORDER = ${util_byte_order}
+
 # Whether libdir is in a path configured into ldconfig
 LIBDIR_IN_LDCONFIG = ${libdir_in_ldconfig}
 
@@ -807,7 +823,9 @@ CONFIGURE_CFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)      \\
 		   -DHAVE_STRSEP=\$(HAVE_STRSEP)                         \\
 		   -DSTD_GETPWUID=\$(STD_GETPWUID)                       \\
 		   -DSTD_ASCTIME=\$(STD_ASCTIME)                         \\
-		   -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)
+		   -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)	 \\
+		   -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
+
 CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     \$(TALLOC_CFLAGS) -DHAVE_VALGRIND=\$(HAVE_VALGRIND) \\
 		     \$(VALGRIND_CFLAGS) \$(XAPIAN_CXXFLAGS)             \\
@@ -815,6 +833,8 @@ CONFIGURE_CXXFLAGS = -DHAVE_GETLINE=\$(HAVE_GETLINE) \$(GMIME_CFLAGS)    \\
 		     -DHAVE_STRSEP=\$(HAVE_STRSEP)                       \\
 		     -DSTD_GETPWUID=\$(STD_GETPWUID)                     \\
 		     -DSTD_ASCTIME=\$(STD_ASCTIME)                       \\
-		     -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)
+		     -DHAVE_XAPIAN_COMPACT=\$(HAVE_XAPIAN_COMPACT)       \\
+		     -DUTIL_BYTE_ORDER=\$(UTIL_BYTE_ORDER)
+
 CONFIGURE_LDFLAGS =  \$(GMIME_LDFLAGS) \$(TALLOC_LDFLAGS) \$(XAPIAN_LDFLAGS)
 EOF
diff --git a/lib/libsha1.c b/lib/libsha1.c
index 87c7c52..aaaa4eb 100644
--- a/lib/libsha1.c
+++ b/lib/libsha1.c
@@ -34,7 +34,7 @@
 */
 
 #include <string.h>     /* for memcpy() etc.        */
-
+#include "endian-util.h"
 #include "libsha1.h"
 
 #if defined(__cplusplus)
@@ -49,20 +49,13 @@ extern "C"
 
 #define bswap_32(x) ((rotr32((x), 24) & 0x00ff00ff) | (rotr32((x), 8) & 0xff00ff00))
 
-/* The macros __BYTE_ORDER__ and __ORDER_*_ENDIAN__ are GNU C
- * extensions. They are also supported by clang as of v3.2 */
-
-#ifdef __BYTE_ORDER__
-#  if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
-#    define bsw_32(p,n) \
-       { int _i = (n); while(_i--) ((uint32_t*)p)[_i] = bswap_32(((uint32_t*)p)[_i]); }
-#  elif (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
-#    define bsw_32(p,n)
-#  else
-#    error "unknown byte order"
-#  endif
+#if (UTIL_BYTE_ORDER == UTIL_ORDER_LITTLE_ENDIAN)
+#  define bsw_32(p,n) \
+     { int _i = (n); while(_i--) ((uint32_t*)p)[_i] = bswap_32(((uint32_t*)p)[_i]); }
+#elif (UTIL_BYTE_ORDER == UTIL_ORDER_BIG_ENDIAN)
+#  define bsw_32(p,n)
 #else
-#    error "macro __BYTE_ORDER__ is not defined"
+#  error "Unsupported byte order"
 #endif
 
 #define SHA1_MASK   (SHA1_BLOCK_SIZE - 1)
diff --git a/util/endian-util.h b/util/endian-util.h
new file mode 100644
index 0000000..bc80c40
--- /dev/null
+++ b/util/endian-util.h
@@ -0,0 +1,38 @@
+/* this file mimics the macros present in recent GCC and CLANG */
+
+#ifndef _ENDIAN_UTIL_H
+#define _ENDIAN_UTIL_H
+
+/* This are prefixed with UTIL to avoid collisions
+ *
+ * You can use something like the following to define UTIL_BYTE_ORDER
+ * in a configure script.
+ */
+#if 0
+#include <stdio.h>
+#include <stdint.h>
+uint32_t test = 0x34333231;
+int main() { printf("%.4s\n", (const char*)&test); return 0; }
+#endif
+
+#define UTIL_ORDER_BIG_ENDIAN	  4321
+#define UTIL_ORDER_LITTLE_ENDIAN  1234
+
+
+#if !defined(UTIL_BYTE_ORDER) || ((UTIL_BYTE_ORDER != UTIL_ORDER_BIG_ENDIAN) && \
+				  (UTIL_BYTE_ORDER != UTIL_ORDER_LITTLE_ENDIAN))
+#undef UTIL_BYTE_ORDER
+#ifdef __BYTE_ORDER__
+#  if (__BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__)
+#    define UTIL_BYTE_ORDER UTIL_ORDER_LITTLE_ENDIAN
+#  elif (__BYTE_ORDER__ == __ORDER_BIG_ENDIAN__)
+#    define UTIL_BYTE_ORDER UTIL_ORDER_BIG_ENDIAN
+#  else
+#    error "Unsupported __BYTE_ORDER__"
+#  endif
+#else
+#  error "UTIL_BYTE_ORDER not correctly defined and __BYTE_ORDER__ not defined."
+#endif
+#endif
+
+#endif
-- 
1.8.4.2