1 files changed, 58 insertions, 0 deletions
diff --git a/core/src/main/java/org/spongycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java b/core/src/main/java/org/spongycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java
new file mode 100644
index 00000000..f7818898
--- /dev/null
+++ b/core/src/main/java/org/spongycastle/crypto/modes/gcm/Tables1kGCMExponentiator.java
@@ -0,0 +1,58 @@
+package org.spongycastle.crypto.modes.gcm;
+
+import java.util.Vector;
+
+import org.spongycastle.util.Arrays;
+
+public class Tables1kGCMExponentiator implements GCMExponentiator
+{
+    // A lookup table of the power-of-two powers of 'x'
+    // - lookupPowX2[i] = x^(2^i)
+    private Vector lookupPowX2;
+
+    public void init(byte[] x)
+    {
+        int[] y = GCMUtil.asInts(x);
+        if (lookupPowX2 != null && Arrays.areEqual(y, (int[])lookupPowX2.elementAt(0)))
+        {
+            return;
+        }
+
+        lookupPowX2 = new Vector(8);
+        lookupPowX2.addElement(y);
+    }
+
+    public void exponentiateX(long pow, byte[] output)
+    {
+        int[] y = GCMUtil.oneAsInts();
+        int bit = 0;
+        while (pow > 0)
+        {
+            if ((pow & 1L) != 0)
+            {
+                ensureAvailable(bit);
+                GCMUtil.multiply(y, (int[])lookupPowX2.elementAt(bit));
+            }
+            ++bit;
+            pow >>>= 1;
+        }
+
+        GCMUtil.asBytes(y, output);
+    }
+
+    private void ensureAvailable(int bit)
+    {
+        int count = lookupPowX2.size();
+        if (count <= bit)
+        {
+            int[] tmp = (int[])lookupPowX2.elementAt(count - 1);
+            do
+            {
+                tmp = Arrays.clone(tmp);
+                GCMUtil.multiply(tmp, tmp);
+                lookupPowX2.addElement(tmp);
+            }
+            while (++count <= bit);
+        }
+    }
+}