polyEval.h

/* Copyright (C) 2012-2020 IBM Corp.
 * This program is Licensed under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance
 * with the License. You may obtain a copy of the License at
 *   http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License. See accompanying LICENSE file.
 */
#ifndef HELIB_POLYEVAL_H
#define HELIB_POLYEVAL_H
 
#include <helib/Context.h>
#include <helib/Ctxt.h>
 
namespace helib {
 
void polyEval(Ctxt& ret, NTL::ZZX poly, const Ctxt& x, long k = 0);
// Note: poly is passed by value, so caller keeps the original
 
void polyEval(Ctxt& ret, const NTL::Vec<Ctxt>& poly, const Ctxt& x);
 
// A useful helper class
 
// This implementation assumes that the size (# of powers) is determined
// at initialization time, it is not hard to grow the std::vector as needed,
// but not clear if there is any application that needs it.
class DynamicCtxtPowers
{
private:
  std::vector<Ctxt> v; // A std::vector storing the powers themselves
 
public:
  DynamicCtxtPowers(const Ctxt& c, long nPowers)
  {
    // Sanity-check
    assertFalse<InvalidArgument>(c.isEmpty(), "Ciphertext cannot be empty");
    assertTrue<InvalidArgument>(nPowers > 0, "Must have positive nPowers");
 
    Ctxt tmp(c.getPubKey(), c.getPtxtSpace());
    v.resize(nPowers, tmp); // Initializes nPowers empty ciphertexts
    v[0] = c;               // store X itself in v[0]
  }
 
  Ctxt& getPower(long e); // must use e >= 1, else throws an exception
 
  Ctxt& at(long i) { return getPower(i + 1); }
  Ctxt& operator[](long i) { return getPower(i + 1); }
 
  const std::vector<Ctxt>& getVector() const { return v; }
  long size() const { return v.size(); }
  bool isPowerComputed(long i)
  {
    return (i > 0 && i <= (long)v.size() && !v[i - 1].isEmpty());
  }
};
 
} // namespace helib
 
#endif // ifndef HELIB_POLYEVAL_H