Compiling the bitfield test with gcc -Wextra generates those warnings:
../../include/babeltrace/bitfield-internal.h:38:45: warning: comparison of
unsigned expression < 0 is always false [-Wtype-limits]
#define _bt_is_signed_type(type) ((type) -1 < (type) 0)
This is the intent of the macro. Disable compiler warnings around use of
that macro.
Signed-off-by: Mathieu Desnoyers <mathieu.desnoy...@efficios.com>
Change-Id: I2dd980e11ebd6cd37ae71b013925a6fca5d7b483
---
Changes since v1:
- Use stdbool.h.
---
include/babeltrace/bitfield-internal.h | 35 ++++++++++++++++++++++++++++++++--
1 file changed, 33 insertions(+), 2 deletions(-)
diff --git a/include/babeltrace/bitfield-internal.h
b/include/babeltrace/bitfield-internal.h
index 5ecde05e..bb0283a3 100644
--- a/include/babeltrace/bitfield-internal.h
+++ b/include/babeltrace/bitfield-internal.h
@@ -24,6 +24,7 @@
*/
#include <stdint.h> /* C99 5.2.4.2 Numerical limits */
+#include <stdbool.h> /* C99 7.16 bool type */
#include <babeltrace/compat/limits-internal.h> /* C99 5.2.4.2 Numerical limits
*/
#include <babeltrace/endian-internal.h> /* Non-standard BIG_ENDIAN,
LITTLE_ENDIAN, BYTE_ORDER */
@@ -40,6 +41,26 @@
#error "bitfield.h requires the compiler representation of signed integers to
be two's complement."
#endif
+/*
+ * _bt_is_signed_type() willingly generates comparison of unsigned
+ * expression < 0, which is always false. Silence compiler warnings.
+ */
+#ifdef __GNUC__
+# define _BT_DIAG_PUSH _Pragma("GCC diagnostic push")
+# define _BT_DIAG_POP _Pragma("GCC diagnostic pop")
+
+# define _BT_DIAG_STRINGIFY_1(x) #x
+# define _BT_DIAG_STRINGIFY(x) _BT_DIAG_STRINGIFY_1(x)
+
+# define _BT_DIAG_IGNORE(option) \
+ _Pragma(_BT_DIAG_STRINGIFY(GCC diagnostic ignored option))
+# define _BT_DIAG_IGNORE_TYPE_LIMITS _BT_DIAG_IGNORE("-Wtype-limits")
+#else
+# define _BT_DIAG_PUSH
+# define _BT_DIAG_POP
+# define _BT_DIAG_IGNORE
+#endif
+
#define _bt_is_signed_type(type) ((type) -1 < (type) 0)
/*
@@ -359,6 +380,7 @@ do {
\
unsigned long ts = sizeof(type) * CHAR_BIT; /* type size */ \
unsigned long start_unit, end_unit, this_unit; \
unsigned long end, cshift; /* cshift is "complement shift" */ \
+ bool is_signed_type; \
\
if (!__length) { \
*__vptr = 0; \
@@ -370,7 +392,11 @@ do {
\
end_unit = (end + (ts - 1)) / ts; \
\
this_unit = end_unit - 1; \
- if (_bt_is_signed_type(__typeof__(__v)) \
+ _BT_DIAG_PUSH \
+ _BT_DIAG_IGNORE_TYPE_LIMITS \
+ is_signed_type = _bt_is_signed_type(__typeof__(__v)); \
+ _BT_DIAG_POP \
+ if (is_signed_type \
&& (__ptr[this_unit] & _bt_lshift((type) 1, (end % ts ? end % ts :
ts) - 1))) \
__v = ~(__typeof__(__v)) 0; \
else \
@@ -426,6 +452,7 @@ do {
\
unsigned long ts = sizeof(type) * CHAR_BIT; /* type size */ \
unsigned long start_unit, end_unit, this_unit; \
unsigned long end, cshift; /* cshift is "complement shift" */ \
+ bool is_signed_type; \
\
if (!__length) { \
*__vptr = 0; \
@@ -437,7 +464,11 @@ do {
\
end_unit = (end + (ts - 1)) / ts; \
\
this_unit = start_unit; \
- if (_bt_is_signed_type(__typeof__(__v)) \
+ _BT_DIAG_PUSH \
+ _BT_DIAG_IGNORE_TYPE_LIMITS \
+ is_signed_type = _bt_is_signed_type(__typeof__(__v)); \
+ _BT_DIAG_POP \
+ if (is_signed_type \
&& (__ptr[this_unit] & _bt_lshift((type) 1, ts - (__start % ts) -
1))) \
__v = ~(__typeof__(__v)) 0; \
else \
--
2.11.0
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