linux-kernel - [PATCH 0/7] lib: bitmap: Simplify bitmap_shift

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Fri, 28 Nov 2014 17:01:03 +0100
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Andrew Morton <akpm@...ux-foundation.org>, Jan Kara <jack@...e.cz>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 0/7] lib: bitmap: Simplify bitmap_shift_{left,right}

I've previously changed the nbits parameter of most bitmap_* functions
to unsigned; now it is bitmap_shift_{left,right}'s turn. This alone
saves some .text, but while at it I found that there were a few other
things one could do. The end result of these seven patches is

$ scripts/bloat-o-meter /tmp/bitmap.o.{old,new}
add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-328 (-328)
function                                     old     new   delta
__bitmap_shift_right                         384     226    -158
__bitmap_shift_left                          306     136    -170

and less importantly also a smaller stack footprint

$ stack-o-meter.pl master bitmap
file                 function                       old  new  delta
lib/bitmap.o         __bitmap_shift_right             24    8  -16
lib/bitmap.o         __bitmap_shift_left              24    0  -24

For each pair of 0 <= shift <= nbits <= 256 I've tested the end result
with a few randomly filled src buffers (including garbage beyond
nbits), in each case verifying that the shift {left,right}-most bits
of dst are zero and the remaining nbits-shift bits correspond to src,
so I'm fairly confident I didn't screw up. That hasn't stopped me from
being wrong before, though.

Rasmus Villemoes (7):
  lib: bitmap: Change bitmap_shift_right to take unsigned parameters
  lib: bitmap: Eliminate branch in __bitmap_shift_right
  lib: bitmap: Remove redundant code from __bitmap_shift_right
  lib: bitmap: Yet another simplification in __bitmap_shift_right
  lib: bitmap: Change bitmap_shift_left to take unsigned parameters
  lib: bitmap: Eliminate branch in __bitmap_shift_left
  lib: bitmap: Remove redundant code from __bitmap_shift_left

 include/linux/bitmap.h | 24 ++++++++++++------------
 lib/bitmap.c           | 47 ++++++++++++++++++++---------------------------
 2 files changed, 32 insertions(+), 39 deletions(-)

-- 
2.0.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/