user/sven/linux.git/include/linux/log2.h, branch v4.10.3

log2: make order_base_2() behave correctly on const input value zero

2017-02-03T17:56:43Z

The function order_base_2() is defined (according to the comment block) as returning zero on input zero, but subsequently passes the input into roundup_pow_of_two(), which is explicitly undefined for input zero. This has gone unnoticed until now, but optimization passes in GCC 7 may produce constant folded function instances where a constant value of zero is passed into order_base_2(), resulting in link errors against the deliberately undefined '____ilog2_NaN'. So update order_base_2() to adhere to its own documented interface. [ See http://marc.info/?l=linux-kernel&m=147672952517795&w=2 and follow-up discussion for more background. The gcc "optimization pass" is really just broken, but now the GCC trunk problem seems to have escaped out of just specially built daily images, so we need to work around it in mainline. - Linus ] Signed-off-by: Ard Biesheuvel Signed-off-by: Linus Torvalds

linux/log2.h: Fix rounddown_pow_of_two(1)

2011-12-13T06:06:55Z

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 Cc: stable@kernel.org Signed-off-by: Linus Torvalds

log2.h: Define order_base_2() macro for convenience.

2008-02-06T18:41:03Z

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 Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Add a "rounddown_pow_of_two" routine to log2.h

2007-10-17T15:42:56Z

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. [m.kozlowski@tuxland.pl: fix unbalanced parentheses] Signed-off-by: Robert P. J. Day Signed-off-by: Mariusz Kozlowski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

Fix roundup_pow_of_two(1)

2007-05-19T03:46:30Z

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 Signed-off-by: Linus Torvalds

Correct trivial typo in log2.h.

2007-02-17T18:17:37Z

Single typo correction in include/linux/log2.h. Signed-off-by: Robert P. J. Day Signed-Off-By: David Howells Signed-off-by: Adrian Bunk

[POWERPC] Add "is_power_of_2" checking to log2.h.

2007-02-07T03:03:19Z

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 Acked-by: Kumar Gala Signed-off-by: Paul Mackerras

[PATCH] LOG2: Alter roundup_pow_of_two() so that it can use a ilog2() on a constant

2006-12-08T16:28:51Z

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 Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] LOG2: Implement a general integer log2 facility in the kernel

2006-12-08T16:28:51Z

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. [akpm@osdl.org: MMC fix] Signed-off-by: David Howells Cc: Benjamin Herrenschmidt Cc: Paul Mackerras Cc: Herbert Xu Cc: David Howells Cc: Wojtek Kaniewski Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds