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/i386/atomic_arch.h b/arch/i386/atomic_arch.h
index 2b1a0490..7d2a48a5 100644
--- a/arch/i386/atomic_arch.h
+++ b/arch/i386/atomic_arch.h
@@ -99,3 +99,10 @@ static inline int a_ctz_l(unsigned long x)
 	__asm__( "bsf %1,%0" : "=r"(r) : "r"(x) );
 	return r;
 }
+
+#define a_clz_32 a_clz_32
+static inline int a_clz_32(uint32_t x)
+{
+	__asm__( "bsr %1,%0 ; xor $31,%0" : "=r"(x) : "r"(x) );
+	return x;
+}