8225603: Enhancement for big integers

Reviewed-by: darcy, ahgross, rhalade

src/java.base/share/classes/java/math/MutableBigInteger.java

@@ -2178,8 +2178,8 @@ class MutableBigInteger {
     }
 
     /**
-     * Calculate the multiplicative inverse of this mod mod, where mod is odd.
-     * This and mod are not changed by the calculation.
+     * Calculate the multiplicative inverse of this modulo mod, where the mod
+     * argument is odd.  This and mod are not changed by the calculation.
      *
      * This method implements an algorithm due to Richard Schroeppel, that uses
      * the same intermediate representation as Montgomery Reduction
@@ -2233,8 +2233,18 @@ class MutableBigInteger {
             k += trailingZeros;
         }
 
-        while (c.sign < 0)
-           c.signedAdd(p);
+        if (c.compare(p) >= 0) { // c has a larger magnitude than p
+            MutableBigInteger remainder = c.divide(p,
+                new MutableBigInteger());
+            // The previous line ignores the sign so we copy the data back
+            // into c which will restore the sign as needed (and converts
+            // it back to a SignedMutableBigInteger)
+            c.copyValue(remainder);
+        }
+
+        if (c.sign < 0) {
+            c.signedAdd(p);
+        }
 
         return fixup(c, p, k);
     }
@@ -2272,8 +2282,8 @@ class MutableBigInteger {
         }
 
         // In theory, c may be greater than p at this point (Very rare!)
-        while (c.compare(p) >= 0)
-            c.subtract(p);
+        if (c.compare(p) >= 0)
+            c = c.divide(p, new MutableBigInteger());
 
         return c;
     }

src/jdk.crypto.ec/share/native/libsunec/impl/mpi.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2007, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2007, 2020, Oracle and/or its affiliates. All rights reserved.
  * Use is subject to license terms.
  *
  * This library is free software; you can redistribute it and/or
@@ -34,7 +34,7 @@
  *   Netscape Communications Corporation
  *   Douglas Stebila <douglas@stebila.ca> of Sun Laboratories.
  *
- * Last Modified Date from the Original Code: Nov 2016
+ * Last Modified Date from the Original Code: Nov 2019
  *********************************************************************** */
 
 /*  Arbitrary precision integer arithmetic library */
@@ -2136,7 +2136,10 @@ mp_err s_mp_almost_inverse(const mp_int *a, const mp_int *p, mp_int *c)
     }
   }
   if (res >= 0) {
-    while (MP_SIGN(c) != MP_ZPOS) {
+    if (s_mp_cmp(c, p) >= 0) {
+      MP_CHECKOK( mp_div(c, p, NULL, c));
+    }
+    if (MP_SIGN(c) != MP_ZPOS) {
       MP_CHECKOK( mp_add(c, p, c) );
     }
     res = k;

test/jdk/java/math/BigInteger/ModInvTime.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2020, 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
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8225603
+ * @summary Tests whether modInverse() completes in a reasonable time
+ * @run main/othervm ModInvTime
+ */
+import java.math.BigInteger;
+
+public class ModInvTime {
+    public static void main(String[] args) throws InterruptedException {
+        BigInteger prime = new BigInteger("39402006196394479212279040100143613805079739270465446667946905279627659399113263569398956308152294913554433653942643");
+        BigInteger s = new BigInteger("9552729729729327851382626410162104591956625415831952158766936536163093322096473638446154604799898109762512409920799");
+        System.out.format("int length: %d, modulus length: %d%n",
+            s.bitLength(), prime.bitLength());
+
+        System.out.println("Computing modular inverse ...");
+        BigInteger mi = s.modInverse(prime);
+        System.out.format("Modular inverse: %s%n", mi);
+        check(s, prime, mi);
+
+        BigInteger ns = s.negate();
+        BigInteger nmi = ns.modInverse(prime);
+        System.out.format("Modular inverse of negation: %s%n", nmi);
+        check(ns, prime, nmi);
+    }
+
+    public static void check(BigInteger val, BigInteger mod, BigInteger inv) {
+        BigInteger r = inv.multiply(val).remainder(mod);
+        if (r.signum() == -1)
+            r = r.add(mod);
+        if (!r.equals(BigInteger.ONE))
+            throw new RuntimeException("Numerically incorrect modular inverse");
+    }
+}