add a_clz_64 helper function

counts leading zero bits of a 64bit int, undefined on zero input.
(has nothing to do with atomics, added to atomic.h so target specific
helper functions are together.)

there is a logarithmic generic implementation and another in terms of
a 32bit a_clz_32 on targets where that's available.

1 files changed, 7 insertions, 0 deletions

diff --git a/arch/powerpc64/atomic_arch.h b/arch/powerpc64/atomic_arch.h
index 269d79c6..17cababd 100644
--- a/arch/powerpc64/atomic_arch.h
+++ b/arch/powerpc64/atomic_arch.h
@@ -61,3 +61,10 @@ static inline void a_crash()
 {
 	__asm__ __volatile__ (".long 0");
 }
+
+#define a_clz_64 a_clz_64
+static inline int a_clz_64(uint64_t x)
+{
+	__asm__ ("cntlzd %0, %1" : "=r"(x) : "r"(x));
+	return x;
+}