// Extract digits from fully packed slots
void extractDigitsPacked(Ctxt& ctxt, long botHigh, long r, long ePrime,
const vector<ZZX>& unpackSlotEncoding)
{
FHE_TIMER_START;
// Step 1: unpack the slots of ctxt
FHE_NTIMER_START(unpack);
ctxt.cleanUp();
// Apply the d automorphisms and store them in scratch area
long d = ctxt.getContext().zMStar.getOrdP();
vector<Ctxt> scratch; // used below
vector<Ctxt> unpacked(d, Ctxt(ZeroCtxtLike, ctxt));
{ // explicit scope to force all temporaries to be released
vector< shared_ptr<DoubleCRT> > coeff_vector;
coeff_vector.resize(d);
for (long i = 0; i < d; i++)
coeff_vector[i] = shared_ptr<DoubleCRT>(new
DoubleCRT(unpackSlotEncoding[i], ctxt.getContext(), ctxt.getPrimeSet()) );
Ctxt tmp1(ZeroCtxtLike, ctxt);
Ctxt tmp2(ZeroCtxtLike, ctxt);
// FIXME: implement using hoisting!
for (long j = 0; j < d; j++) { // process jth Frobenius
tmp1 = ctxt;
tmp1.frobeniusAutomorph(j);
tmp1.cleanUp();
// FIXME: not clear if we should call cleanUp here
for (long i = 0; i < d; i++) {
tmp2 = tmp1;
tmp2.multByConstant(*coeff_vector[mcMod(i+j, d)]);
unpacked[i] += tmp2;
}
}
}
FHE_NTIMER_STOP(unpack);
// Step 2: extract the digits top-1,...,0 from the slots of unpacked[i]
long p = ctxt.getContext().zMStar.getP();
long p2r = power_long(p,r);
long topHigh = botHigh + r-1;
#ifdef DEBUG_PRINTOUT
cerr << "+ After unpack ";
decryptAndPrint(cerr, unpacked[0], *dbgKey, *dbgEa, printFlag);
cerr << " extracting "<<(topHigh+1)<<" digits\n";
#endif
if (p==2 && r>2)
topHigh--; // For p==2 we sometime get a bit for free
FHE_NTIMER_START(extractDigits);
for (long i=0; i<(long)unpacked.size(); i++) {
if (topHigh<=0) { // extracting LSB = no-op
scratch.assign(1,unpacked[i]);
} else { // extract digits topHigh...0, store them in scratch
extractDigits(scratch, unpacked[i], topHigh+1);
}
// set upacked[i] = -\sum_{j=botHigh}^{topHigh} scratch[j] * p^{j-botHigh}
if (topHigh >= (long)scratch.size()) {
topHigh = scratch.size() -1;
cerr << " @ suspect: not enough digits in extractDigitsPacked\n";
}
unpacked[i] = scratch[topHigh];
for (long j=topHigh-1; j>=botHigh; --j) {
unpacked[i].multByP();
unpacked[i] += scratch[j];
}
if (p==2 && botHigh>0) // For p==2, subtract also the previous bit
unpacked[i] += scratch[botHigh-1];
unpacked[i].negate();
if (r>ePrime) { // Add in digits from the bottom part, if any
long topLow = r-1 - ePrime;
Ctxt tmp = scratch[topLow];
for (long j=topLow-1; j>=0; --j) {
tmp.multByP();
tmp += scratch[j];
}
if (ePrime>0)
tmp.multByP(ePrime); // multiply by p^e'
unpacked[i] += tmp;
}
unpacked[i].reducePtxtSpace(p2r); // Our plaintext space is now mod p^r
}
FHE_NTIMER_STOP(extractDigits);
#ifdef DEBUG_PRINTOUT
cerr << "+ Before repack ";
decryptAndPrint(cerr, unpacked[0], *dbgKey, *dbgEa, printFlag);
#endif
// Step 3: re-pack the slots
FHE_NTIMER_START(repack);
const EncryptedArray& ea2 = *ctxt.getContext().ea;
ZZX xInSlots;
vector<ZZX> xVec(ea2.size());
ctxt = unpacked[0];
for (long i=1; i<d; i++) {
x2iInSlots(xInSlots, i, xVec, ea2);
unpacked[i].multByConstant(xInSlots);
ctxt += unpacked[i];
}
FHE_NTIMER_STOP(repack);
}
// Extract digits from thinly packed slots
void extractDigitsThin(Ctxt& ctxt, long botHigh, long r, long ePrime)
{
FHE_TIMER_START;
Ctxt unpacked(ctxt);
unpacked.cleanUp();
vector<Ctxt> scratch;
// Step 2: extract the digits top-1,...,0 from the slots of unpacked[i]
long p = ctxt.getContext().zMStar.getP();
long p2r = power_long(p,r);
long topHigh = botHigh + r-1;
#ifdef DEBUG_PRINTOUT
cerr << "+ After unpack ";
decryptAndPrint(cerr, unpacked, *dbgKey, *dbgEa, printFlag);
cerr << " extracting "<<(topHigh+1)<<" digits\n";
#endif
if (p==2 && r>2)
topHigh--; // For p==2 we sometime get a bit for free
if (topHigh<=0) { // extracting LSB = no-op
scratch.assign(1, unpacked);
} else { // extract digits topHigh...0, store them in scratch
extractDigits(scratch, unpacked, topHigh+1);
}
// set upacked = -\sum_{j=botHigh}^{topHigh} scratch[j] * p^{j-botHigh}
if (topHigh >= LONG(scratch.size())) {
topHigh = scratch.size() -1;
cerr << " @ suspect: not enough digits in extractDigitsPacked\n";
}
unpacked = scratch[topHigh];
for (long j=topHigh-1; j>=botHigh; --j) {
unpacked.multByP();
unpacked += scratch[j];
}
if (p==2 && botHigh>0) // For p==2, subtract also the previous bit
unpacked += scratch[botHigh-1];
unpacked.negate();
if (r>ePrime) { // Add in digits from the bottom part, if any
long topLow = r-1 - ePrime;
Ctxt tmp = scratch[topLow];
for (long j=topLow-1; j>=0; --j) {
tmp.multByP();
tmp += scratch[j];
}
if (ePrime>0)
tmp.multByP(ePrime); // multiply by p^e'
unpacked += tmp;
}
unpacked.reducePtxtSpace(p2r); // Our plaintext space is now mod p^r
#ifdef DEBUG_PRINTOUT
cerr << "+ Before repack ";
decryptAndPrint(cerr, unpacked[0], *dbgKey, *dbgEa, printFlag);
#endif
ctxt = unpacked;
}
