[PATCH] Introduce a boolean "single_bit_set" function.

Robert P. J. Day
2009-04-23T17:44:41Z

A boolean single_bit_set() routine would simplify the numerous
constructs of the form (((n & (n - 1)) == 0)) when testing for
single-bitness.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>

---

This is similar to the current is_power_of_2() routine defined in
include/linux/log2.h, which is mathematically identical but,
semantically, should be defined independently just so the code is more
readable.

I'm open to an alternative function name.

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 6182913..1c0c840 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -45,6 +45,13 @@ static inline unsigned long hweight_long(unsigned long w)
return sizeof(w) == 4 ? hweight32(w) : hweight64(w);
}

+static inline __attribute__((const))
+bool single_bit_set(unsigned long n)
+{
+ return (n != 0 && ((n & (n - 1)) == 0));
+}
+
+
/**
* rol32 - rotate a 32-bit value left
* @word: value to rotate