[PATCH v2 04/11] util: MAX_FROM_BITS() should be unsigned

[David Gibson <david@gibson.dropbear.id.au>]

MAX_FROM_BITS() computes the maximum value representable in a number of
bits.  The expression for that is an unsigned value, but we explicitly cast
it to a signed int.  It looks like this is because one of the main users is
for FD_REF_MAX, which is used to bound fd values, typically stored as a
signed int.

The value MAX_FROM_BITS() is calculating is naturally non-negative, though,
so it makes more sense for it to be unsigned, and to move the case to the
definition of FD_REF_MAX.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 passt.h | 2 +-
 util.h  | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/passt.h b/passt.h
index 3f5dfb9..0fce637 100644
--- a/passt.h
+++ b/passt.h
@@ -87,7 +87,7 @@ union epoll_ref {
 	struct {
 		enum epoll_type type:8;
 #define FD_REF_BITS		24
-#define FD_REF_MAX		MAX_FROM_BITS(FD_REF_BITS)
+#define FD_REF_MAX		((int)MAX_FROM_BITS(FD_REF_BITS))
 		int32_t		fd:FD_REF_BITS;
 		union {
 			union tcp_epoll_ref tcp;
diff --git a/util.h b/util.h
index 78a8fb2..b1106e8 100644
--- a/util.h
+++ b/util.h
@@ -42,7 +42,7 @@
 #define ROUND_DOWN(x, y)	((x) & ~((y) - 1))
 #define ROUND_UP(x, y)		(((x) + (y) - 1) & ~((y) - 1))
 
-#define MAX_FROM_BITS(n)	((int)((1U << (n)) - 1))
+#define MAX_FROM_BITS(n)	(((1U << (n)) - 1))
 
 #define BIT(n)			(1UL << (n))
 #define BITMAP_BIT(n)		(BIT((n) % (sizeof(long) * 8)))
-- 
2.43.0