Replace log2 with MostSignificantBit

src/utils.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 68 matching lines @@
     case 4: bits++;  // Fall through.
     case 2: bits++;  // Fall through.
     case 1: break;
   }
   ASSERT_EQ(1 << bits, original_x);
   return bits;
   return 0;
 }
 
 
+inline int MostSignificantBit(uint32_t x) {
+  static const int msb4[] = {0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4};
+  int nibble = 0;
+  if (x & 0xffff0000) {
+    nibble += 16;
+    x >>= 16;
+  }
+  if (x & 0xff00) {
+    nibble += 8;
+    x >>= 8;
+  }
+  if (x & 0xf0) {
+    nibble += 4;
+    x >>= 4;
+  }
+  return nibble + msb4[x];
+}
+
+
 // Magic numbers for integer division.
 // These are kind of 2's complement reciprocal of the divisors.
 // Details and proofs can be found in:
 // - Hacker's Delight, Henry S. Warren, Jr.
 // - The PowerPC Compiler Writer’s Guide
 // and probably many others.
 // See details in the implementation of the algorithm in
 // lithium-codegen-arm.cc : LCodeGen::TryEmitSignedIntegerDivisionByConstant().
 struct DivMagicNumbers {
   unsigned M;
@@ skipping 1010 matching lines @@
 
   // Every compiled stub starts with this id.
   static const int kStubEntryId = 5;
 
   int id_;
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_UTILS_H_