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__.

Reviewed-by: Nícolas F. R. A. Prado <[email protected]>
Tested-by: Diederik de Haas <[email protected]>
Acked-by: Andy Shevchenko <[email protected]>
Reviewed-by: AngeloGioacchino Del Regno <[email protected]>
Signed-off-by: Cristian Ciocaltea <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Daniel Stone <[email protected]>

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.

include/uapi/linux/const.h

@@ -50,4 +50,22 @@
 
 #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 */