| Age | Commit message (Collapse) | Author | Files | Lines |
|---|
|
Exactly like roundup_pow_of_two(1), the rounddown version was buggy for
the case of a compile-time constant '1' argument. Probably because it
originated from the same code, sharing history with the roundup version
from before the bugfix (for that one, see commit 1a06a52ee1b0: "Fix
roundup_pow_of_two(1)").
However, unlike the roundup version, the fix for rounddown is to just
remove the broken special case entirely. It's simply not needed - the
generic code
1UL << ilog2(n)
does the right thing for the constant '1' argment too. The only reason
roundup needed that special case was because rounding up does so by
subtracting one from the argument (and then adding one to the result)
causing the obvious problems with "ilog2(0)".
But rounddown doesn't do any of that, since ilog2() naturally truncates
(ie "rounds down") to the right rounded down value. And without the
ilog2(0) case, there's no reason for the special case that had the wrong
value.
tl;dr: rounddown_pow_of_two(1) should be 1, not 0.
Acked-by: Dmitry Torokhov <[email protected]>
Cc: [email protected]
Signed-off-by: Linus Torvalds <[email protected]>
|
|
Given a number of places in the tree that need to calculate this value
explicitly, might as well just create a macro for it.
(akpm: must be implemented as a macro for callee typeof() usage)
Signed-off-by: Robert P. J. Day <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
|
|
To go along with the existing "roundup_pow_of_two" routine, add one for
rounding down since that operation appears to crop up on a regular basis in
the source tree.
[[email protected]: fix unbalanced parentheses]
Signed-off-by: Robert P. J. Day <[email protected]>
Signed-off-by: Mariusz Kozlowski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
|
|
1 is a power of two, therefore roundup_pow_of_two(1) should return 1. It does
in case the argument is a variable but in case it's a constant it behaves
wrong and returns 0. Probably nobody ever did it so this was never noticed.
Signed-off-by: Rolf Eike Beer <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
|
|
Single typo correction in include/linux/log2.h.
Signed-off-by: Robert P. J. Day <[email protected]>
Signed-Off-By: David Howells <[email protected]>
Signed-off-by: Adrian Bunk <[email protected]>
|
|
Add the inline function "is_power_of_2()" to log2.h, where the value
zero is *not* considered to be a power of two.
Signed-off-by: Robert P. J. Day <[email protected]>
Acked-by: Kumar Gala <[email protected]>
Signed-off-by: Paul Mackerras <[email protected]>
|
|
constant
Alter roundup_pow_of_two() so that it can make use of ilog2() on a constant to
produce a constant value, retaining the ability for an arch to override it in
the non-const case.
This permits the function to be used to initialise variables.
Signed-off-by: David Howells <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
|
|
This facility provides three entry points:
ilog2() Log base 2 of unsigned long
ilog2_u32() Log base 2 of u32
ilog2_u64() Log base 2 of u64
These facilities can either be used inside functions on dynamic data:
int do_something(long q)
{
...;
y = ilog2(x)
...;
}
Or can be used to statically initialise global variables with constant values:
unsigned n = ilog2(27);
When performing static initialisation, the compiler will report "error:
initializer element is not constant" if asked to take a log of zero or of
something not reducible to a constant. They treat negative numbers as
unsigned.
When not dealing with a constant, they fall back to using fls() which permits
them to use arch-specific log calculation instructions - such as BSR on
x86/x86_64 or SCAN on FRV - if available.
[[email protected]: MMC fix]
Signed-off-by: David Howells <[email protected]>
Cc: Benjamin Herrenschmidt <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Herbert Xu <[email protected]>
Cc: David Howells <[email protected]>
Cc: Wojtek Kaniewski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
|