Program Listing for File coefpackedencoding.cpp

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// Copyright (c) 2014-2022, NJIT, Duality Technologies Inc. and other contributors
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/*
  Represents and defines packing integers of plaintext objects into polynomial coefficients in OpenFHE
 */

#include "encoding/coefpackedencoding.h"
#include "constants.h"

namespace lbcrypto {

template <typename P>
inline static void encodeVec(P& poly, const PlaintextModulus& mod, int64_t lb, int64_t ub,
                             const std::vector<int64_t>& value, SCHEME schemeID) {
    if (ub > INT32_MAX || lb < INT32_MIN)
        OPENFHE_THROW("Cannot encode a coefficient larger than 32 bits");

    poly.SetValuesToZero();
    for (size_t i = 0; i < value.size() && i < poly.GetLength(); i++) {
        if (value[i] <= lb || value[i] > ub)
            OPENFHE_THROW("Cannot encode integer " + std::to_string(value[i]) + " at position " + std::to_string(i) +
                          " because it is out of range of plaintext modulus " + std::to_string(mod));

        typename P::Integer entry{value[i]};

        if (value[i] < 0) {
            if (schemeID == SCHEME::BFVRNS_SCHEME) {
                // TODO: Investigate why this doesn't work with q instead of t.
                uint64_t adjustedVal{mod - static_cast<uint64_t>(llabs(value[i]))};
                entry = typename P::Integer(adjustedVal);
            }
            else {
                // It is more efficient to encode negative numbers using the ciphertext
                // modulus no noise growth occurs
                entry = poly.GetModulus() - typename P::Integer(static_cast<uint64_t>(llabs(value[i])));
            }
        }
        poly[i] = entry;
    }
}

bool CoefPackedEncoding::Encode() {
    if (this->isEncoded)
        return true;
    PlaintextModulus mod     = this->encodingParams->GetPlaintextModulus();
    NativeInteger originalSF = scalingFactorInt;
    for (size_t j = 1; j < noiseScaleDeg; j++) {
        scalingFactorInt = scalingFactorInt.ModMul(originalSF, mod);
    }

    if (this->typeFlag == IsNativePoly) {
        encodeVec(this->encodedNativeVector, mod, LowBound(), HighBound(), this->value, this->GetSchemeID());
        encodedNativeVector = encodedNativeVector.Times(scalingFactorInt);
    }
    else {
        encodeVec(this->encodedVector, mod, LowBound(), HighBound(), this->value, this->GetSchemeID());
    }

    if (this->typeFlag == IsDCRTPoly) {
        this->encodedVectorDCRT = this->encodedVector;
        encodedVectorDCRT       = encodedVectorDCRT.Times(scalingFactorInt);
    }

    this->isEncoded = true;
    return true;
}

template <typename P>
inline static void fillVec(const P& poly, const PlaintextModulus& mod, std::vector<int64_t>& value) {
    value.clear();
    value.reserve(poly.GetLength());

    int64_t half                 = int64_t(mod) / 2;
    const typename P::Integer& q = poly.GetModulus();
    typename P::Integer qHalf    = q >> 1;

    for (size_t i = 0; i < poly.GetLength(); i++) {
        int64_t val;
        if (poly[i] > qHalf)
            val = (-(q - poly[i]).ConvertToInt());
        else
            val = poly[i].ConvertToInt();
        if (val > half)
            val -= mod;
        value.push_back(val);
    }
}

bool CoefPackedEncoding::Decode() {
    PlaintextModulus mod = this->encodingParams->GetPlaintextModulus();

    if (this->typeFlag == IsNativePoly) {
        NativeInteger scfInv = scalingFactorInt.ModInverse(mod);
        NativePoly temp      = encodedNativeVector.Times(scfInv).Mod(mod);
        fillVec(temp, mod, this->value);
    }
    else {
        fillVec(this->encodedVector, mod, this->value);
    }

    return true;
}

} /* namespace lbcrypto */