Replace log2 with MostSignificantBit

src/utils.h

Index: src/utils.h
diff --git a/src/utils.h b/src/utils.h
index b16730b8c46d750c1e264ad07713868c2b32d804..5680384196d2c870cd519f420d34bb84337fb881 100644
--- a/src/utils.h
+++ b/src/utils.h
@@ -86,6 +86,25 @@ inline int WhichPowerOf2(uint32_t x) {
 }
 
 
+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: