From 625e870b4fb7ff4caf4d8a4614e9bda7c174b291 Mon Sep 17 00:00:00 2001 From: David Herrmann Date: Tue, 13 May 2014 19:47:58 +0200 Subject: 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! --- src/shared/macro.h | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'src/shared') 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])) /* -- cgit v1.2.3-54-g00ecf