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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);
}
}
}
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