Various QUIC cleanups to sync with internal code.

net/quic/congestion_control/cubic.cc

Index: net/quic/congestion_control/cubic.cc
diff --git a/net/quic/congestion_control/cubic.cc b/net/quic/congestion_control/cubic.cc
index 3d03b9f60d1249af6a6c808e6ee6624ff2852a19..221209886cd98420d75e516a9c53e590d8c388a6 100644
--- a/net/quic/congestion_control/cubic.cc
+++ b/net/quic/congestion_control/cubic.cc
@@ -9,9 +9,14 @@
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/time/time.h"
+#include "net/quic/congestion_control/cube_root.h"
+#include "net/quic/quic_protocol.h"
+
+using std::max;
 
 namespace net {
 
+namespace {
 // Constants based on TCP defaults.
 // The following constants are in 2^10 fractions of a second instead of ms to
 // allow a 10 shift right to divide.
@@ -25,52 +30,6 @@ const uint32 kBetaSPDY = 939;  // Back off factor after loss for SPDY, reduces
                                // the CWND by 1/12th.
 const uint32 kBetaLastMax = 871;  // Additional back off factor after loss for
                                   // the stored max value.
-
-namespace {
-// Find last bit in a 64-bit word.
-int FindMostSignificantBit(uint64 x) {
-  if (!x) {
-    return 0;
-  }
-  int r = 0;
-  if (x & 0xffffffff00000000ull) {
-    x >>= 32;
-    r += 32;
-  }
-  if (x & 0xffff0000u) {
-    x >>= 16;
-    r += 16;
-  }
-  if (x & 0xff00u) {
-    x >>= 8;
-    r += 8;
-  }
-  if (x & 0xf0u) {
-    x >>= 4;
-    r += 4;
-  }
-  if (x & 0xcu) {
-    x >>= 2;
-    r += 2;
-  }
-  if (x & 0x02u) {
-    x >>= 1;
-    r++;
-  }
-  if (x & 0x01u) {
-    r++;
-  }
-  return r;
-}
-
-// 6 bits table [0..63]
-const uint32 cube_root_table[] = {
-    0,  54,  54,  54, 118, 118, 118, 118, 123, 129, 134, 138, 143, 147, 151,
-  156, 157, 161, 164, 168, 170, 173, 176, 179, 181, 185, 187, 190, 192, 194,
-  197, 199, 200, 202, 204, 206, 209, 211, 213, 215, 217, 219, 221, 222, 224,
-  225, 227, 229, 231, 232, 234, 236, 237, 239, 240, 242, 244, 245, 246, 248,
-  250, 251, 252, 254
-};
 }  // namespace
 
 Cubic::Cubic(const QuicClock* clock)
@@ -80,34 +39,6 @@ Cubic::Cubic(const QuicClock* clock)
   Reset();
 }
 
-// Calculate the cube root using a table lookup followed by one Newton-Raphson
-// iteration.
-uint32 Cubic::CubeRoot(uint64 a) {
-  uint32 msb = FindMostSignificantBit(a);
-  DCHECK_LE(msb, 64u);
-
-  if (msb < 7) {
-    // MSB in our table.
-    return ((cube_root_table[static_cast<uint32>(a)]) + 31) >> 6;
-  }
-  // MSB          7,  8,  9, 10, 11, 12, 13, 14, 15, 16, ...
-  // cubic_shift  1,  1,  1,  2,  2,  2,  3,  3,  3,  4, ...
-  uint32 cubic_shift = (msb - 4);
-  cubic_shift = ((cubic_shift * 342) >> 10);  // Div by 3, biased high.
-
-  // 4 to 6 bits accuracy depending on MSB.
-  uint32 down_shifted_to_6bit = (a >> (cubic_shift * 3));
-  uint64 root = ((cube_root_table[down_shifted_to_6bit] + 10) << cubic_shift)
-      >> 6;
-
-  // Make one Newton-Raphson iteration.
-  // Since x has an error (inaccuracy due to the use of fix point) we get a
-  // more accurate result by doing x * (x - 1) instead of x * x.
-  root = 2 * root + (a / (root * (root - 1)));
-  root = ((root * 341) >> 10);  // Div by 3, biased low.
-  return static_cast<uint32>(root);
-}
-
 void Cubic::Reset() {
   epoch_ = QuicTime::Zero();  // Reset time.
   last_update_time_ = QuicTime::Zero();  // Reset time.
@@ -143,8 +74,8 @@ QuicTcpCongestionWindow Cubic::CongestionWindowAfterAck(
   // Cubic is "independent" of RTT, the update is limited by the time elapsed.
   if (last_congestion_window_ == current_congestion_window &&
       (current_time.Subtract(last_update_time_) <= MaxCubicTimeInterval())) {
-    return std::max(last_target_congestion_window_,
-                    estimated_tcp_congestion_window_);
+    return max(last_target_congestion_window_,
+               estimated_tcp_congestion_window_);
   }
   last_congestion_window_ = current_congestion_window;
   last_update_time_ = current_time;
@@ -160,7 +91,7 @@ QuicTcpCongestionWindow Cubic::CongestionWindowAfterAck(
       time_to_origin_point_ = 0;
       origin_point_congestion_window_ = current_congestion_window;
     } else {
-      time_to_origin_point_ = CubeRoot(kCubeFactor *
+      time_to_origin_point_ = CubeRoot::Root(kCubeFactor *
           (last_max_congestion_window_ - current_congestion_window));
       origin_point_congestion_window_ =
           last_max_congestion_window_;