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authorDavid Herrmann <dh.herrmann@gmail.com>2014-05-13 19:47:58 +0200
committerDavid Herrmann <dh.herrmann@gmail.com>2014-05-13 22:05:32 +0200
commit625e870b4fb7ff4caf4d8a4614e9bda7c174b291 (patch)
tree733373c564bac30ae2c0f4e2a38ae6f44431e19c
parentead349509e325aad720bb0349521a9e56e2ac7c0 (diff)
shared: add ALIGN_POWER2 macro
Sounds easy, turns out to be horrible to implement: ALIGN_POWER2 returns the next higher power of 2. clz(0) is undefined, same is true for left-shift-overflows, yey, C rocks!
-rw-r--r--src/shared/macro.h13
-rw-r--r--src/test/test-util.c31
2 files changed, 44 insertions, 0 deletions
diff --git a/src/shared/macro.h b/src/shared/macro.h
index d53b07fea5..53bd578d7e 100644
--- a/src/shared/macro.h
+++ b/src/shared/macro.h
@@ -100,6 +100,19 @@ static inline size_t ALIGN_TO(size_t l, size_t ali) {
#define ALIGN_TO_PTR(p, ali) ((void*) ALIGN_TO((unsigned long) p, ali))
+/* align to next higher power-of-2 (except for: 0 => 0, overflow => 0) */
+static inline unsigned long ALIGN_POWER2(unsigned long u) {
+ /* clz(0) is undefined */
+ if (u == 1)
+ return 1;
+
+ /* left-shift overflow is undefined */
+ if (__builtin_clzl(u - 1UL) < 1)
+ return 0;
+
+ return 1UL << (sizeof(u) * 8 - __builtin_clzl(u - 1UL));
+}
+
#define ELEMENTSOF(x) (sizeof(x)/sizeof((x)[0]))
/*
diff --git a/src/test/test-util.c b/src/test/test-util.c
index 93929cd9fc..caf8d2b12b 100644
--- a/src/test/test-util.c
+++ b/src/test/test-util.c
@@ -37,6 +37,36 @@ static void test_streq_ptr(void) {
assert_se(!streq_ptr("abc", "cdef"));
}
+static void test_align_power2(void) {
+ unsigned long i, p2;
+
+ assert_se(ALIGN_POWER2(0) == 0);
+ assert_se(ALIGN_POWER2(1) == 1);
+ assert_se(ALIGN_POWER2(2) == 2);
+ assert_se(ALIGN_POWER2(3) == 4);
+ assert_se(ALIGN_POWER2(12) == 16);
+
+ assert_se(ALIGN_POWER2(ULONG_MAX) == 0);
+ assert_se(ALIGN_POWER2(ULONG_MAX - 1) == 0);
+ assert_se(ALIGN_POWER2(ULONG_MAX - 1024) == 0);
+ assert_se(ALIGN_POWER2(ULONG_MAX / 2) == ULONG_MAX / 2 + 1);
+ assert_se(ALIGN_POWER2(ULONG_MAX + 1) == 0);
+
+ for (i = 1; i < 131071; ++i) {
+ for (p2 = 1; p2 < i; p2 <<= 1)
+ /* empty */ ;
+
+ assert_se(ALIGN_POWER2(i) == p2);
+ }
+
+ for (i = ULONG_MAX - 1024; i < ULONG_MAX; ++i) {
+ for (p2 = 1; p2 && p2 < i; p2 <<= 1)
+ /* empty */ ;
+
+ assert_se(ALIGN_POWER2(i) == p2);
+ }
+}
+
static void test_first_word(void) {
assert_se(first_word("Hello", ""));
assert_se(first_word("Hello", "Hello"));
@@ -680,6 +710,7 @@ int main(int argc, char *argv[]) {
log_open();
test_streq_ptr();
+ test_align_power2();
test_first_word();
test_close_many();
test_parse_boolean();