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author | Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com> | 2008-06-12 10:47:56 +0200 |
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committer | Ingo Molnar <mingo@elte.hu> | 2008-06-12 10:47:56 +0200 |
commit | f595ec964daf7f99668039d7303ddedd09a75142 (patch) | |
tree | 4ee6679105f0437995ff200f10885598921ae1cd /lib | |
parent | 5e70b7f3c24468bb1635b295945edb48ecd9656a (diff) | |
download | op-kernel-dev-f595ec964daf7f99668039d7303ddedd09a75142.zip op-kernel-dev-f595ec964daf7f99668039d7303ddedd09a75142.tar.gz |
common implementation of iterative div/mod
We have a few instances of the open-coded iterative div/mod loop, used
when we don't expcet the dividend to be much bigger than the divisor.
Unfortunately modern gcc's have the tendency to strength "reduce" this
into a full mod operation, which isn't necessarily any faster, and
even if it were, doesn't exist if gcc implements it in libgcc.
The workaround is to put a dummy asm statement in the loop to prevent
gcc from performing the transformation.
This patch creates a single implementation of this loop, and uses it
to replace the open-coded versions I know about.
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Segher Boessenkool <segher@kernel.crashing.org>
Cc: Christian Kujau <lists@nerdbynature.de>
Cc: Robert Hancock <hancockr@shaw.ca>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'lib')
-rw-r--r-- | lib/div64.c | 23 |
1 files changed, 23 insertions, 0 deletions
diff --git a/lib/div64.c b/lib/div64.c index bb5bd0c..76c0154 100644 --- a/lib/div64.c +++ b/lib/div64.c @@ -98,3 +98,26 @@ EXPORT_SYMBOL(div64_u64); #endif #endif /* BITS_PER_LONG == 32 */ + +/* + * Iterative div/mod for use when dividend is not expected to be much + * bigger than divisor. + */ +u32 iter_div_u64_rem(u64 dividend, u32 divisor, u64 *remainder) +{ + u32 ret = 0; + + while (dividend >= divisor) { + /* The following asm() prevents the compiler from + optimising this loop into a modulo operation. */ + asm("" : "+rm"(dividend)); + + dividend -= divisor; + ret++; + } + + *remainder = dividend; + + return ret; +} +EXPORT_SYMBOL(iter_div_u64_rem); |