Tweaks for speed in integer arithmetic runtime.

runtime/platform/utils.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/utils.h"
 
 namespace dart {
 
 // Implementation is from "Hacker's Delight" by Henry S. Warren, Jr.,
 // figure 3-3, page 48, where the function is called clp2.
@@ skipping 17 matching lines @@
   x = x - ((x >> 1) & 0x55555555);
   x = (x & 0x33333333) + ((x >> 2) & 0x33333333);
   x = (x + (x >> 4)) & 0x0F0F0F0F;
   x = x + (x >> 8);
   x = x + (x >> 16);
   return static_cast<int>(x & 0x0000003F);
 }
 
 
 int Utils::HighestBit(int64_t v) {
-  uint64_t t = static_cast<uint64_t>((v > 0) ? v : -v);
-  int count = 0;
-  while ((t >>= 1) != 0) {
-    count++;
-  }
-  return count;
+  uint64_t x = static_cast<uint64_t>((v > 0) ? v : -v);
+  uint64_t t;
+  int r = 0;
+  if ((t = x >> 32) != 0) { x = t; r += 32; }
+  if ((t = x >> 16) != 0) { x = t; r += 16; }
+  if ((t = x >> 8) != 0) { x = t; r += 8; }
+  if ((t = x >> 4) != 0) { x = t; r += 4; }
+  if ((t = x >> 2) != 0) { x = t; r += 2; }
+  if (x > 1) r += 1;
+  return r;
 }
 
 
 uint32_t Utils::StringHash(const char* data, int length) {
   // This implementation is based on the public domain MurmurHash
   // version 2.0. It assumes that the underlying CPU can read from
   // unaligned addresses. The constants M and R have been determined
   // to work well experimentally.
   // TODO(3158902): need to account for unaligned address access on ARM.
   const uint32_t M = 0x5bd1e995;
@@ skipping 42 matching lines @@
   a = (a ^ 0xc761c23c) ^ (a >> 19);
   a = (a + 0x165667b1) + (a << 5);
   a = (a + 0xd3a2646c) ^ (a << 9);
   a = (a + 0xfd7046c5) + (a << 3);
   a = (a ^ 0xb55a4f09) ^ (a >> 16);
   return static_cast<uint32_t>(a);
 }
 
 
 }  // namespace dart