[TCP] tcp_cubic: faster cube root

[powerpc.git] / net / ipv4 / tcp_cubic.c

diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c
index 9a582fb..0e6cdfe 100644 (file)
--- a/net/ipv4/tcp_cubic.c
+++ b/net/ipv4/tcp_cubic.c
@@ -51,8 +51,6 @@ MODULE_PARM_DESC(bic_scale, "scale (scaled by 1024) value for bic function (bic_
 module_param(tcp_friendliness, int, 0644);
 MODULE_PARM_DESC(tcp_friendliness, "turn on/off tcp friendliness");
 
-#include <asm/div64.h>
-
 /* BIC TCP Parameters */
 struct bictcp {
        u32     cnt;            /* increase cwnd by 1 after ACKs */
@@ -93,49 +91,22 @@ static void bictcp_init(struct sock *sk)
                tcp_sk(sk)->snd_ssthresh = initial_ssthresh;
 }
 
-/* 64bit divisor, dividend and result. dynamic precision */
-static inline u_int64_t div64_64(u_int64_t dividend, u_int64_t divisor)
-{
-       u_int32_t d = divisor;
-
-       if (divisor > 0xffffffffULL) {
-               unsigned int shift = fls(divisor >> 32);
-
-               d = divisor >> shift;
-               dividend >>= shift;
-       }
-
-       /* avoid 64 bit division if possible */
-       if (dividend >> 32)
-               do_div(dividend, d);
-       else
-               dividend = (uint32_t) dividend / d;
-
-       return dividend;
-}
-
 /*
  * calculate the cubic root of x using Newton-Raphson
  */
 static u32 cubic_root(u64 a)
 {
-       u32 x, x1;
+       u32 x;
 
        /* Initial estimate is based on:
         * cbrt(x) = exp(log(x) / 3)
         */
        x = 1u << (fls64(a)/3);
 
-       /*
-        * Iteration based on:
-        *                         2
-        * x    = ( 2 * x  +  a / x  ) / 3
-        *  k+1          k         k
-        */
-       do {
-               x1 = x;
-               x = (2 * x + (uint32_t) div64_64(a, x*x)) / 3;
-       } while (abs(x1 - x) > 1);
+       /* converges to 32 bits in 3 iterations */
+       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;
 }