Optimize memory size calculation

@@ -204,16 +204,11 @@ TR_malloc(size_t size)
             size = 1 << (MIN_BITS - 1);
             idx = 0;
         } else {
-            size_t mask;
-
-            idx   = TR_bitwidth(size);
-            mask  = (1 << (idx + 1)) - 1;
+			// size-1 to ensure that powers of two will not be
+			// changed to the next power of two
+            idx   = TR_bitwidth(size-1) + 1;
+			size  = 1 << idx;
             idx  -= (MIN_BITS - 1);
-
-            if (size != (size & ~(mask >> 1))) {
-                size = (size << 1) & ~mask;
-                idx++;
-            }
         }
     }