4837946: Faster multiplication and exponentiation of large integers

4646474: BigInteger.pow() algorithm slow in 1.4.0
Summary: Implement Karatsuba and 3-way Toom-Cook multiplication as well as exponentiation using Karatsuba and Toom-Cook squaring.
Reviewed-by: alanb, bpb, martin
Contributed-by: NAlan Eliasen <eliasen@mindspring.com>

src/share/classes/java/math/BigDecimal.java

 /*
- * Copyright (c) 1996, 2011, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -3538,24 +3538,7 @@ public class BigDecimal extends Number implements Comparable<BigDecimal> {
                 return expandBigIntegerTenPowers(n);
         }
 
-        if (n < 1024*524288) {
-            // BigInteger.pow is slow, so make 10**n by constructing a
-            // BigInteger from a character string (still not very fast)
-            // which occupies no more than 1GB (!) of memory.
-            char tenpow[] = new char[n + 1];
-            tenpow[0] = '1';
-            for (int i = 1; i <= n; i++) {
-                tenpow[i] = '0';
-            }
-            return new BigInteger(tenpow, 1, tenpow.length);
-        }
-
-        if ((n & 0x1) == 0x1) {
-            return BigInteger.TEN.multiply(bigTenToThe(n - 1));
-        } else {
-            BigInteger tmp = bigTenToThe(n/2);
-            return tmp.multiply(tmp);
-        }
+        return BigInteger.TEN.pow(n);
     }
 
     /**