linux-kernel - [PATCH v3 1/4] uapi: Provide DIV_ROUND

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Message-Id: <20251118-rk3588-bgcolor-v3-1-a2cc909428ea@collabora.com>
Date: Tue, 18 Nov 2025 01:51:59 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Sandy Huang <hjc@...k-chips.com>, 
 Heiko Stübner <heiko@...ech.de>, 
 Andy Yan <andy.yan@...k-chips.com>, 
 Louis Chauvet <louis.chauvet@...tlin.com>, 
 Haneen Mohammed <hamohammed.sa@...il.com>, 
 Melissa Wen <melissa.srw@...il.com>
Cc: Robert Mader <robert.mader@...labora.com>, kernel@...labora.com, 
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org
Subject: [PATCH v3 1/4] uapi: Provide DIV_ROUND_CLOSEST()

Currently DIV_ROUND_CLOSEST() is only available for the kernel via
include/linux/math.h.

Expose it to userland as well by adding __KERNEL_DIV_ROUND_CLOSEST() as
a common definition in uapi.

Additionally, ensure it allows building ISO C applications by switching
from the 'typeof' GNU extension to the ISO-friendly __typeof__.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
---
 include/linux/math.h       | 18 +-----------------
 include/uapi/linux/const.h | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/include/linux/math.h b/include/linux/math.h
index 0198c92cbe3e..24bb868f971c 100644
--- a/include/linux/math.h
+++ b/include/linux/math.h
@@ -89,23 +89,7 @@
 }							\
 )
 
-/*
- * Divide positive or negative dividend by positive or negative divisor
- * and round to closest integer. Result is undefined for negative
- * divisors if the dividend variable type is unsigned and for negative
- * dividends if the divisor variable type is unsigned.
- */
-#define DIV_ROUND_CLOSEST(x, divisor)(			\
-{							\
-	typeof(x) __x = x;				\
-	typeof(divisor) __d = divisor;			\
-	(((typeof(x))-1) > 0 ||				\
-	 ((typeof(divisor))-1) > 0 ||			\
-	 (((__x) > 0) == ((__d) > 0))) ?		\
-		(((__x) + ((__d) / 2)) / (__d)) :	\
-		(((__x) - ((__d) / 2)) / (__d));	\
-}							\
-)
+#define DIV_ROUND_CLOSEST __KERNEL_DIV_ROUND_CLOSEST
 /*
  * Same as above but for u64 dividends. divisor must be a 32-bit
  * number.
diff --git a/include/uapi/linux/const.h b/include/uapi/linux/const.h
index b8f629ef135f..471877322f47 100644
--- a/include/uapi/linux/const.h
+++ b/include/uapi/linux/const.h
@@ -50,4 +50,21 @@
 
 #define __KERNEL_DIV_ROUND_UP(n, d) (((n) + (d) - 1) / (d))
 
+/*
+ * Divide positive or negative dividend by positive or negative divisor
+ * and round to closest integer. Result is undefined for negative
+ * divisors if the dividend variable type is unsigned and for negative
+ * dividends if the divisor variable type is unsigned.
+ */
+#define __KERNEL_DIV_ROUND_CLOSEST(x, divisor)(		\
+{							\
+	__typeof__(x) __x = x;				\
+	__typeof__(divisor) __d = divisor;		\
+	(((__typeof__(x))-1) > 0 ||			\
+	 ((__typeof__(divisor))-1) > 0 ||		\
+	 (((__x) > 0) == ((__d) > 0))) ?		\
+		(((__x) + ((__d) / 2)) / (__d)) :	\
+		(((__x) - ((__d) / 2)) / (__d));	\
+}							\
+)
 #endif /* _UAPI_LINUX_CONST_H */

-- 
2.51.2