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

Things like 3619dec510 ("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: Kees 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Kees Cook 2018-08-21 21:55:28 -07:00 committed by Linus Torvalds
parent 96c6a32ccb
commit cedc5b6aab
1 changed files with 34 additions and 1 deletions
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35
include/linux/kernel.h
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@ -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); \