[PATCH] bswap: convert to unsigned before shifting in get_be32

["René Scharfe" <l.s.r@web.de>]

The pointer p is dereferenced and we get an unsigned char.  Before
shifting it's automatically promoted to int.  Left-shifting a signed
32-bit value bigger than 127 by 24 places is undefined.  Explicitly
convert to a 32-bit unsigned type to avoid undefined behaviour if
the highest bit is set.

Found with Clang's UBSan.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
 compat/bswap.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/compat/bswap.h b/compat/bswap.h
index d47c003544..4582c1107a 100644
--- a/compat/bswap.h
+++ b/compat/bswap.h
@@ -166,10 +166,10 @@ static inline uint64_t git_bswap64(uint64_t x)
 	(*((unsigned char *)(p) + 0) << 8) | \
 	(*((unsigned char *)(p) + 1) << 0) )
 #define get_be32(p)	( \
-	(*((unsigned char *)(p) + 0) << 24) | \
-	(*((unsigned char *)(p) + 1) << 16) | \
-	(*((unsigned char *)(p) + 2) <<  8) | \
-	(*((unsigned char *)(p) + 3) <<  0) )
+	((uint32_t)*((unsigned char *)(p) + 0) << 24) | \
+	((uint32_t)*((unsigned char *)(p) + 1) << 16) | \
+	((uint32_t)*((unsigned char *)(p) + 2) <<  8) | \
+	((uint32_t)*((unsigned char *)(p) + 3) <<  0) )
 #define put_be32(p, v)	do { \
 	unsigned int __v = (v); \
 	*((unsigned char *)(p) + 0) = __v >> 24; \
-- 
2.13.3