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

rev 12150 : 8046943: JEP 246: Leverage CPU Instructions for GHASH and RSA
Summary: Add montgomeryMultiply intrinsic
Reviewed-by: kvn

@@ -2063,10 +2063,25 @@
         t *= 2 - val*t;
         return t;
     }
 
     /**
+     * Returns the multiplicative inverse of val mod 2^64.  Assumes val is odd.
+     */
+    static long inverseMod64(long val) {
+        // Newton's iteration!
+        long t = val;
+        t *= 2 - val*t;
+        t *= 2 - val*t;
+        t *= 2 - val*t;
+        t *= 2 - val*t;
+        t *= 2 - val*t;
+        assert(t * val == 1);
+        return t;
+    }
+
+    /**
      * Calculate the multiplicative inverse of 2^k mod mod, where mod is odd.
      */
     static MutableBigInteger modInverseBP2(MutableBigInteger mod, int k) {
         // Copy the mod to protect original
         return fixup(new MutableBigInteger(1), new MutableBigInteger(mod), k);