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authorJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>2008-06-12 10:47:56 +0200
committerIngo Molnar <mingo@elte.hu>2008-06-12 10:47:56 +0200
commitf595ec964daf7f99668039d7303ddedd09a75142 (patch)
tree4ee6679105f0437995ff200f10885598921ae1cd /lib/div64.c
parent5e70b7f3c24468bb1635b295945edb48ecd9656a (diff)
downloadleg-kernel-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/div64.c')
-rw-r--r--lib/div64.c23
1 files changed, 23 insertions, 0 deletions
diff --git a/lib/div64.c b/lib/div64.c
index bb5bd0c0f030..76c01542d3e1 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);