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author | Daniel Borkmann <dborkman@redhat.com> | 2014-01-22 02:29:40 +0100 |
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committer | David S. Miller <davem@davemloft.net> | 2014-01-21 23:17:20 -0800 |
commit | 89770b0a69ee0e0e5e99c722192d535115f73778 (patch) | |
tree | a8c96a91c2417dc81f5ce08aa59ebcfd456e0335 /include/linux/kernel.h | |
parent | f337db64af059c9a94278a8b0ab97d87259ff62f (diff) | |
download | linux-stable-89770b0a69ee0e0e5e99c722192d535115f73778.tar.gz linux-stable-89770b0a69ee0e0e5e99c722192d535115f73778.tar.bz2 linux-stable-89770b0a69ee0e0e5e99c722192d535115f73778.zip |
net: introduce reciprocal_scale helper and convert users
As David Laight suggests, we shouldn't necessarily call this
reciprocal_divide() when users didn't requested a reciprocal_value();
lets keep the basic idea and call it reciprocal_scale(). More
background information on this topic can be found in [1].
Joint work with Hannes Frederic Sowa.
[1] http://homepage.cs.uiowa.edu/~jones/bcd/divide.html
Suggested-by: David Laight <david.laight@aculab.com>
Cc: Jakub Zawadzki <darkjames-ws@darkjames.pl>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/kernel.h')
-rw-r--r-- | include/linux/kernel.h | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index ecb87544cc5d..03d8a6b0e2e8 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -193,6 +193,25 @@ extern int _cond_resched(void); (__x < 0) ? -__x : __x; \ }) +/** + * reciprocal_scale - "scale" a value into range [0, ep_ro) + * @val: value + * @ep_ro: right open interval endpoint + * + * Perform a "reciprocal multiplication" in order to "scale" a value into + * range [0, ep_ro), where the upper interval endpoint is right-open. + * This is useful, e.g. for accessing a index of an array containing + * ep_ro elements, for example. Think of it as sort of modulus, only that + * the result isn't that of modulo. ;) Note that if initial input is a + * small value, then result will return 0. + * + * Return: a result based on val in interval [0, ep_ro). + */ +static inline u32 reciprocal_scale(u32 val, u32 ep_ro) +{ + return (u32)(((u64) val * ep_ro) >> 32); +} + #if defined(CONFIG_MMU) && \ (defined(CONFIG_PROVE_LOCKING) || defined(CONFIG_DEBUG_ATOMIC_SLEEP)) void might_fault(void); |