// Add/subtract a ciphertext part to a ciphertext.
// With negative=true we subtract, otherwise we add.
void Ctxt::addPart(const DoubleCRT& part, const SKHandle& handle,
bool matchPrimeSet, bool negative)
{
FHE_TIMER_START;
assert (&part.getContext() == &context);
if (parts.size()==0) { // inserting 1st part
primeSet = part.getIndexSet();
parts.push_back(CtxtPart(part,handle));
if (negative) parts.back().Negate(); // not thread-safe??
}
else { // adding to a ciphertext with existing parts
if (!(part.getIndexSet() <= primeSet)) {
// add to the the prime-set of *this, if needed (this is expensive)
if (matchPrimeSet) {
IndexSet setDiff = part.getIndexSet() / primeSet; // set minus
for (size_t i=0; i<parts.size(); i++) parts[i].addPrimes(setDiff);
primeSet.insert(setDiff);
}
else // this should never happen
throw std::logic_error("part has too many primes and matchPrimeSet==false");
}
DoubleCRT tmp(context, IndexSet::emptySet());
const DoubleCRT* ptr = ∂
// mod-UP the part if needed
IndexSet s = primeSet / part.getIndexSet();
if (!empty(s)) { // if need to mod-UP, do it on a temporary copy
tmp = part;
tmp.addPrimesAndScale(s);
ptr = &tmp;
}
long j = getPartIndexByHandle(handle);
if (j>=0) { // found a matching part, add them up
if (negative) parts[j] -= *ptr;
else parts[j] += *ptr;
} else { // no mathing part found, just append this part
parts.push_back(CtxtPart(*ptr,handle));
if (negative) parts.back().Negate(); // not thread-safe??
}
}
}
// Dummy encryption, this procedure just encodes the plaintext in a Ctxt object
void Ctxt::DummyEncrypt(const ZZX& ptxt, double size)
{
if (size < 0.0) {
size = ((double) context.zMStar.getPhiM()) * ptxtSpace*ptxtSpace /12.0;
}
noiseVar = size;
primeSet = context.ctxtPrimes;
// A single part, with the plaintext as data and handle pointing to 1
long f = rem(context.productOfPrimes(context.ctxtPrimes),ptxtSpace);
if (f == 1) { // scale by constant
DoubleCRT dcrt(ptxt, context, primeSet);
parts.assign(1, CtxtPart(dcrt));
} else {
ZZX tmp;
MulMod(tmp, ptxt, f, ptxtSpace, /*positive=*/false);
DoubleCRT dcrt(tmp, context, primeSet);
parts.assign(1, CtxtPart(dcrt));
}
}
