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8225603: Enhancement for big integers
Reviewed-by: darcy, ahgross, rhalade
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Brian Burkhalter committed Oct 29, 2019
1 parent 14c0c19 commit 833a3897dced3bcc435589ebbbd1047076b2fe8e
Showing 3 changed files with 79 additions and 9 deletions.
@@ -2178,8 +2178,8 @@ static MutableBigInteger modInverseBP2(MutableBigInteger mod, int k) {
}

/**
* 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 @@ private MutableBigInteger modInverse(MutableBigInteger mod) {
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 @@ static MutableBigInteger fixup(MutableBigInteger c, MutableBigInteger p,
}

// 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;
}
@@ -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;
@@ -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");
}
}

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