On Mon, Jul 08, 2024 at 09:29:38PM +0530, Devarsh Thakkar wrote: > Add below rounding related macros: > > round_closest_up(x, y) : Rounds x to closest multiple of y where y is a > power of 2, with a preference to round up in case two nearest values are > possible. > > round_closest_down(x, y) : Rounds x to closest multiple of y where y is a > power of 2, with a preference to round down in case two nearest values are > possible. > > roundclosest(x, y) : Rounds x to closest multiple of y, this macro should > generally be used only when y is not multiple of 2 as otherwise > round_closest* macros should be used which are much faster. > > Examples: > * round_closest_up(17, 4) = 16 > * round_closest_up(15, 4) = 16 > * round_closest_up(14, 4) = 16 > * round_closest_down(17, 4) = 16 > * round_closest_down(15, 4) = 16 > * round_closest_down(14, 4) = 12 > * roundclosest(21, 5) = 20 > * roundclosest(19, 5) = 20 > * roundclosest(17, 5) = 15 > > Signed-off-by: Devarsh Thakkar <devarsht@xxxxxx> > Acked-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx> > --- > NOTE: This patch is inspired from the Mentor Graphics IPU driver [1] > which uses similar macro locally and which is updated in further patch > in the series to use this generic macro instead along with other drivers > having similar requirements. > > Link: https://elixir.bootlin.com/linux/v6.8.9/source/drivers/gpu/ipu-v3/ipu-image-convert.c#L480 [1] > --- > include/linux/math.h | 63 ++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 63 insertions(+) > > diff --git a/include/linux/math.h b/include/linux/math.h > index dd4152711de7..79e3dfda77fc 100644 > --- a/include/linux/math.h > +++ b/include/linux/math.h > @@ -34,6 +34,52 @@ > */ > #define round_down(x, y) ((x) & ~__round_mask(x, y)) > > +/** > + * round_closest_up - round closest to be multiple of specified value (which is > + * power of 2) with preference to rounding up > + * @x: the value to round > + * @y: multiple to round closest to (must be a power of 2) > + * > + * Rounds @x to closest multiple of @y (which must be a power of 2). > + * The value can be either rounded up or rounded down depending upon rounded > + * value's closeness to the specified value. If there are two closest possible > + * values, i.e. the difference between the specified value and it's rounded up > + * and rounded down values is same then preference is given to rounded up > + * value. > + * > + * To perform arbitrary rounding to closest value (not multiple of 2), use > + * roundclosest(). > + * > + * Examples: > + * * round_closest_up(17, 4) = 16 > + * * round_closest_up(15, 4) = 16 > + * * round_closest_up(14, 4) = 16 > + */ > +#define round_closest_up(x, y) round_down((x) + (y) / 2, (y)) > + > +/** > + * round_closest_down - round closest to be multiple of specified value (which > + * is power of 2) with preference to rounding down > + * @x: the value to round > + * @y: multiple to round closest to (must be a power of 2) > + * > + * Rounds @x to closest multiple of @y (which must be a power of 2). > + * The value can be either rounded up or rounded down depending upon rounded > + * value's closeness to the specified value. If there are two closest possible > + * values, i.e. the difference between the specified value and it's rounded up > + * and rounded down values is same then preference is given to rounded up > + * value. > + * > + * To perform arbitrary rounding to closest value (not multiple of 2), use > + * roundclosest(). > + * > + * Examples: > + * * round_closest_down(17, 4) = 16 > + * * round_closest_down(15, 4) = 16 > + * * round_closest_down(14, 4) = 12 > + */ > +#define round_closest_down(x, y) round_up((x) - (y) / 2, (y)) > + Naming aside, is there an actual use case for having both roundclosest() and round_closest_up() today? (i.e., is there any potential caller that would actually care about the rounding direction for borderline cases?) > #define DIV_ROUND_UP __KERNEL_DIV_ROUND_UP > > #define DIV_ROUND_DOWN_ULL(ll, d) \ > @@ -77,6 +123,23 @@ > } \ > ) > > +/** > + * roundclosest - round to nearest multiple > + * @x: the value to round > + * @y: multiple to round nearest to > + * > + * Rounds @x to nearest multiple of @y. > + * The rounded value can be greater than or less than @x depending > + * upon it's nearness to @x. If @y will always be a power of 2, consider > + * using the faster round_closest_up() or round_closest_down(). > + * > + * Examples: > + * * roundclosest(21, 5) = 20 > + * * roundclosest(19, 5) = 20 > + * * roundclosest(17, 5) = 15 > + */ > +#define roundclosest(x, y) rounddown((x) + (y) / 2, (y)) Won't this go wrong if (x) + (y) / 2 overflows? This may happen even in some cases where the correctly rounded value would be in range. The existing rounddown() already leaves something to be desired IIUC: if given a negative dividend, it looks like it actually rounds up, at least on some arches. But maybe people don't use it that way very often. Perhaps I'm missing something. [...] Cheers ---Dave
