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!

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]))
 
 /*