On Friday 25 June 2021 17:22:31 Geert Uytterhoeven wrote:

Hi Pali,

On Fri, Jun 25, 2021 at 4:37 PM Pali Rohár [off-list ref] wrote:

quoted

Provide DIV_U64_ROUND_CLOSEST helper which uses div_u64 to perform
division rounded to the closest integer using unsigned 64bit
dividend and unsigned 32bit divisor.

Signed-off-by: Pali Rohár <pali@kernel.org>

Thanks for your patch!

quoted

--- a/include/linux/math64.h
+++ b/include/linux/math64.h

@@ -281,6 +281,19 @@ u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div);
 #define DIV64_U64_ROUND_CLOSEST(dividend, divisor)     \
        ({ u64 _tmp = (divisor); div64_u64((dividend) + _tmp / 2, _tmp); })

+/*
+ * DIV_U64_ROUND_CLOSEST - unsigned 64bit divide with 32bit divisor rounded to nearest integer
+ * @dividend: unsigned 64bit dividend
+ * @divisor: unsigned 32bit divisor
+ *
+ * Divide unsigned 64bit dividend by unsigned 32bit divisor
+ * and round to closest integer.
+ *
+ * Return: dividend / divisor rounded to nearest integer
+ */
+#define DIV_U64_ROUND_CLOSEST(dividend, divisor)       \
+       ({ u32 _tmp = (divisor); div_u64((u64)(dividend) + _tmp / 2, _tmp); })

Given "dividend" should already be an unsigned 64-bit value, I don't
think the cast to "u64" is needed. Similar macros in this file also
don't have the cast.

It is just to ensure that plus operation between dividend and _tmp is
evaluated in 64-bit context to prevent overflow. Just a case when user
calls this macro with 32-bit dividend param. As it is a macro (and not
inline function) type is not automatically enforced.

DIV_S64_ROUND_CLOSEST macro assigns its argument into temporary 64-bit
variable which then ensures usage of 64-bit arithmetic operations. Same
applies for DIV64_U64_ROUND_CLOSEST and DIV64_U64_ROUND_UP macros.

So this is reason why I added explicit cast to u64.

quoted

+
 /*
  * DIV_S64_ROUND_CLOSEST - signed 64bit divide with 32bit divisor rounded to nearest integer
  * @dividend: signed 64bit dividend

With the above nit fixed:
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds