linux-kernel - [PATCH 1/4] bitops: Add single_bit

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Date:   Mon, 22 Nov 2021 13:03:25 +0200
From:   Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
To:     Matti Vaittinen <mazziesaccount@...il.com>,
        Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jiri Kosina <trivial@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 1/4] bitops: Add single_bit_set()

There are cases when it is useful to check a bit-mask has only one bit
set. Add a generic helper for it instead of baking own one for each
user.

Signed-off-by: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>
---
I am not at all sure what would be the best place for this. Please let
me know if you think some other file would be more appropriate.
---
 include/linux/bitops.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/include/linux/bitops.h b/include/linux/bitops.h
index 5e62e2383b7f..dd6c7baed3d3 100644
--- a/include/linux/bitops.h
+++ b/include/linux/bitops.h
@@ -66,6 +66,26 @@ extern unsigned long __sw_hweight64(__u64 w);
 	     (start) < (size); \
 	     (start) = find_next_clump8(&(clump), (bits), (size), (start) + 8))
 
+/**
+ * single_bit_set - check if only one bit is set in value
+ * @bits:		value to check
+ * @bits_to_check:	how many bits we should scan
+ *
+ * Return: true if only one of the checked bits is set, othervice return false.
+ */
+static inline bool single_bit_set(const unsigned long bits, int bits_to_check)
+{
+	int bit;
+
+	bit = find_first_bit(&bits, bits_to_check);
+	if (bit == bits_to_check)
+		return false;
+
+	bit = find_next_bit(&bits, bits_to_check, bit + 1);
+
+	return (bit == bits_to_check);
+}
+
 static inline int get_bitmask_order(unsigned int count)
 {
 	int order;
-- 
2.31.1


-- 
Matti Vaittinen, Linux device drivers
ROHM Semiconductors, Finland SWDC
Kiviharjunlenkki 1E
90220 OULU
FINLAND

~~~ "I don't think so," said Rene Descartes. Just then he vanished ~~~
Simon says - in Latin please.
~~~ "non cogito me" dixit Rene Descarte, deinde evanescavit ~~~
Thanks to Simon Glass for the translation =] 

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