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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 /src/shared/macro.h
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!
Diffstat (limited to 'src/shared/macro.h')
-rw-r--r--src/shared/macro.h13
1 files changed, 13 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]))
/*