From: David Bremner <david@tethera.net>

Previously PLATFORM_BYTE_ORDER and IS_LITTLE_ENDIAN were not defined,
so the little endian code was always compiled in.

This will have the effect that the "SHA1s" on big endian architectures
will change (i.e. become actual sha1s). So someone re-indexing their
database could conceivable lose tags on messages without a message-id
header.
---
 lib/libsha1.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/lib/libsha1.c b/lib/libsha1.c
index 5d16f6a..794854b 100644
--- a/lib/libsha1.c
+++ b/lib/libsha1.c
@@ -49,11 +49,17 @@ extern "C"
 
 #define bswap_32(x) ((rotr32((x), 24) & 0x00ff00ff) | (rotr32((x), 8) & 0xff00ff00))
 
-#if (PLATFORM_BYTE_ORDER == IS_LITTLE_ENDIAN)
-#define bsw_32(p,n) \
-    { int _i = (n); while(_i--) ((uint32_t*)p)[_i] = bswap_32(((uint32_t*)p)[_i]); }
+#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
 #else
-#define bsw_32(p,n)
+#    error "macro __BYTE_ORDER__ is not defined"
 #endif
 
 #define SHA1_MASK   (SHA1_BLOCK_SIZE - 1)
-- 
1.8.4.2