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Commit cedc5b6a authored by Kees Cook's avatar Kees Cook Committed by Linus Torvalds
Browse files

kernel.h: documentation for roundup() vs round_up() 

Things like 3619dec5 ("dh key: fix rounding up KDF output length")
expose the lack of explicit documentation for roundup() vs round_up().  At
least we can try to document it better if anyone goes looking.

Link: http://lkml.kernel.org/r/20180703041950.GA43464@beast


Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 96c6a32c

include/linux/kernel.h

+34 −1
Original line number Diff line number Diff line
@@ -85,7 +85,23 @@ 
 * arguments just once each.

 */

#define __round_mask(x, y) ((__typeof__(x))((y)-1))

/**

 * round_up - round up to next specified power of 2

 * @x: the value to round

 * @y: multiple to round up to (must be a power of 2)

 *

 * Rounds @x up to next multiple of @y (which must be a power of 2).

 * To perform arbitrary rounding up, use roundup() below.

 */

#define round_up(x, y) ((((x)-1) | __round_mask(x, y))+1)

/**

 * round_down - round down to next specified power of 2

 * @x: the value to round

 * @y: multiple to round down to (must be a power of 2)

 *

 * Rounds @x down to next multiple of @y (which must be a power of 2).

 * To perform arbitrary rounding down, use rounddown() below.

 */

#define round_down(x, y) ((x) & ~__round_mask(x, y))



/**
@@ -110,13 +126,30 @@ 
# define DIV_ROUND_UP_SECTOR_T(ll,d) DIV_ROUND_UP(ll,d)

#endif



/* The `const' in roundup() prevents gcc-3.3 from calling __divdi3 */

/**

 * roundup - round up to the next specified multiple

 * @x: the value to up

 * @y: multiple to round up to

 *

 * Rounds @x up to next multiple of @y. If @y will always be a power

 * of 2, consider using the faster round_up().

 *

 * The `const' here prevents gcc-3.3 from calling __divdi3

 */

#define roundup(x, y) (					\

{							\

	const typeof(y) __y = y;			\

	(((x) + (__y - 1)) / __y) * __y;		\

}							\

)

/**

 * rounddown - round down to next specified multiple

 * @x: the value to round

 * @y: multiple to round down to

 *

 * Rounds @x down to next multiple of @y. If @y will always be a power

 * of 2, consider using the faster round_down().

 */

#define rounddown(x, y) (				\

{							\

	typeof(x) __x = (x);				\