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Subject[PATCH] tcp_cubic: use 32 bit math
The basic calculation has to be done in 32 bits to avoid
doing 64 bit divide by 3. The value x is only 22bits max
so only need full 64 bits only for x^2.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>

---
net/ipv4/tcp_cubic.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)
--- net-2.6.22.orig/net/ipv4/tcp_cubic.c 2007-03-07 15:51:37.000000000 -0800
+++ net-2.6.22/net/ipv4/tcp_cubic.c 2007-03-07 17:06:02.000000000 -0800
@@ -96,7 +96,7 @@
*/
static u32 cubic_root(u64 a)
{
- u64 x;
+ u32 x;

/* Initial estimate is based on:
* cbrt(x) = exp(log(x) / 3)
@@ -104,9 +104,9 @@
x = 1u << (fls64(a)/3);

/* converges to 32 bits in 3 iterations */
- x = (2 * x + div64_64(a, x*x)) / 3;
- x = (2 * x + div64_64(a, x*x)) / 3;
- x = (2 * x + div64_64(a, x*x)) / 3;
+ x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3;
+ x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3;
+ x = (2 * x + (u32)div64_64(a, (u64)x*(u64)x)) / 3;

return x;
}
-
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