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using System;
using System.Collections;
using Org.BouncyCastle.Utilities;
namespace Org.BouncyCastle.Crypto.Modes.Gcm
{
public class Tables1kGcmExponentiator
: IGcmExponentiator
{
// A lookup table of the power-of-two powers of 'x'
// - lookupPowX2[i] = x^(2^i)
private IList lookupPowX2;
public void Init(byte[] x)
{
ulong[] y = GcmUtilities.AsUlongs(x);
if (lookupPowX2 != null && Arrays.AreEqual(y, (ulong[])lookupPowX2[0]))
return;
lookupPowX2 = Platform.CreateArrayList(8);
lookupPowX2.Add(y);
}
public void ExponentiateX(long pow, byte[] output)
{
ulong[] y = GcmUtilities.OneAsUlongs();
int bit = 0;
while (pow > 0)
{
if ((pow & 1L) != 0)
{
EnsureAvailable(bit);
GcmUtilities.Multiply(y, (ulong[])lookupPowX2[bit]);
}
++bit;
pow >>= 1;
}
GcmUtilities.AsBytes(y, output);
}
private void EnsureAvailable(int bit)
{
int count = lookupPowX2.Count;
if (count <= bit)
{
ulong[] tmp = (ulong[])lookupPowX2[count - 1];
do
{
tmp = Arrays.Clone(tmp);
GcmUtilities.Square(tmp, tmp);
lookupPowX2.Add(tmp);
}
while (++count <= bit);
}
}
}
}
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