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authorDavid Herrmann <dh.herrmann@gmail.com>2014-08-15 16:54:52 +0200
committerDavid Herrmann <dh.herrmann@gmail.com>2014-08-15 16:59:09 +0200
commit7242d7420b04132f93f1426ec713f9b09bdeba54 (patch)
tree79937cb4843d701f1f7c6fdb6b954a9c9a720925
parentfdcba430aeae442ab0ea12a08d96cfc3d13f57ef (diff)
macro: add CONST_MAX() macro
The CONST_MAX() macro is similar to MAX(), but verifies that both arguments have the same type and are constant expressions. Furthermore, the result of CONST_MAX() is again a constant-expression. CONST_MAX() avoids any statement-expressions and other non-trivial expression-types. This avoids rather arbitrary restrictions in both GCC and LLVM, which both either fail with statement-expressions inside type-declarations or statement-expressions inside static-const initializations. If anybody knows how to circumvent this, please feel free to unify CONST_MAX() and MAX().
-rw-r--r--src/shared/macro.h9
-rw-r--r--src/test/test-util.c23
2 files changed, 32 insertions, 0 deletions
diff --git a/src/shared/macro.h b/src/shared/macro.h
index 11bd8b3a93..179b24c983 100644
--- a/src/shared/macro.h
+++ b/src/shared/macro.h
@@ -140,6 +140,15 @@ static inline unsigned long ALIGN_POWER2(unsigned long u) {
_a > _b ? _a : _b; \
})
+/* evaluates to (void) if _A or _B are not constant or of different types */
+#define CONST_MAX(_A, _B) \
+ __extension__ (__builtin_choose_expr( \
+ __builtin_constant_p(_A) && \
+ __builtin_constant_p(_B) && \
+ __builtin_types_compatible_p(typeof(_A), typeof(_B)), \
+ ((_A) > (_B)) ? (_A) : (_B), \
+ (void)0))
+
#define MAX3(x,y,z) \
__extension__ ({ \
const typeof(x) _c = MAX(x,y); \
diff --git a/src/test/test-util.c b/src/test/test-util.c
index 7d81b0b7be..a8fa48aed2 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -70,6 +70,28 @@ static void test_align_power2(void) {
}
}
+static void test_max(void) {
+ static const struct {
+ int a;
+ int b[CONST_MAX(10, 100)];
+ } val1 = {
+ .a = CONST_MAX(10, 100),
+ };
+ int d = 0;
+
+ assert_cc(sizeof(val1.b) == sizeof(int) * 100);
+
+ /* CONST_MAX returns (void) instead of a value if the passed arguments
+ * are not of the same type or not constant expressions. */
+ assert_cc(__builtin_types_compatible_p(typeof(CONST_MAX(1, 10)), int));
+ assert_cc(__builtin_types_compatible_p(typeof(CONST_MAX(d, 10)), void));
+ assert_cc(__builtin_types_compatible_p(typeof(CONST_MAX(1, 1U)), void));
+
+ assert_se(val1.a == 100);
+ assert_se(MAX(++d, 0) == 1);
+ assert_se(d == 1);
+}
+
static void test_first_word(void) {
assert_se(first_word("Hello", ""));
assert_se(first_word("Hello", "Hello"));
@@ -927,6 +949,7 @@ int main(int argc, char *argv[]) {
test_streq_ptr();
test_align_power2();
+ test_max();
test_first_word();
test_close_many();
test_parse_boolean();