Re: [PATCH v5 1/4] uapi: Provide DIV_ROUND_CLOSEST()

Jani Nikula
2026-01-27T13:58:43Z

On Tue, 27 Jan 2026, Cristian Ciocaltea <cristian.ciocaltea@collabora.com> wrote:
> 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__.

I am not convinced that it's a good idea to make the implementation of
kernel DIV_ROUND_CLOSEST() part of the kernel UAPI, which is what this
change effectively does.

I'd at least like to get an ack from Andy Shevchenko first (Cc'd).

BR,
Jani.

> Reviewed-by: Nícolas F. R. A. Prado <nfraprado@collabora.com>
> Tested-by: Diederik de Haas <diederik@cknow-tech.com>
> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.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 6dc1d1d32fbc..1e8fb3efbc8c 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 */

--
Jani Nikula, Intel