[PATCH v3.1 3/9] lib: Introduce macros for bit operations

[Austin Clements <aclements@csail.mit.edu>]

These macros help clarify basic bit-twiddling code and are written to
be robust against C undefined behavior of shift operators.
---
 lib/message.cc        |  6 +++---
 lib/notmuch-private.h | 11 +++++++++++
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/lib/message.cc b/lib/message.cc
index 38bc929..55d2ff6 100644
--- a/lib/message.cc
+++ b/lib/message.cc
@@ -869,7 +869,7 @@ notmuch_bool_t
 notmuch_message_get_flag (notmuch_message_t *message,
 			  notmuch_message_flag_t flag)
 {
-    return message->flags & (1 << flag);
+    return NOTMUCH_TEST_BIT (message->flags, flag);
 }
 
 void
@@ -877,9 +877,9 @@ notmuch_message_set_flag (notmuch_message_t *message,
 			  notmuch_message_flag_t flag, notmuch_bool_t enable)
 {
     if (enable)
-	message->flags |= (1 << flag);
+	NOTMUCH_SET_BIT (&message->flags, flag);
     else
-	message->flags &= ~(1 << flag);
+	NOTMUCH_CLEAR_BIT (&message->flags, flag);
 }
 
 time_t
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 36cc12b..b86897c 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -63,6 +63,17 @@ NOTMUCH_BEGIN_DECLS
 #define STRNCMP_LITERAL(var, literal) \
     strncmp ((var), (literal), sizeof (literal) - 1)
 
+/* Robust bit test/set/reset macros */
+#define NOTMUCH_TEST_BIT(val, bit) \
+    (((bit) < 0 || (bit) >= CHAR_BIT * sizeof (unsigned long long)) ? 0	\
+     : !!((val) & (1ull << (bit))))
+#define NOTMUCH_SET_BIT(valp, bit) \
+    (((bit) < 0 || (bit) >= CHAR_BIT * sizeof (unsigned long long)) ? *(valp) \
+     : (*(valp) |= (1ull << (bit))))
+#define NOTMUCH_CLEAR_BIT(valp,  bit) \
+    (((bit) < 0 || (bit) >= CHAR_BIT * sizeof (unsigned long long)) ? *(valp) \
+     : (*(valp) &= ~(1ull << (bit))))
+
 #define unused(x) x __attribute__ ((unused))
 
 #ifdef __cplusplus
-- 
2.1.0