void replicate0(const EncryptedArray& ea, Ctxt& ctxt, long pos)
{
long dim = ea.dimension();
for (long d = 0; d < dim; d++) {
if (!ea.nativeDimension(d)) {
long shamt = -ea.coordinate(d, pos);
ea.rotate1D(ctxt, d, shamt, true); // "don't care"
}
Ctxt ctxt_orig = ctxt;
long sz = ea.sizeOfDimension(d);
long k = NumBits(sz);
long e = 1;
// now process bits k-2 down to 0
for (long j = k-2; j >= 0; j--) {
// e -> 2*e
Ctxt tmp = ctxt;
ea.rotate1D(tmp, d, e, true); // "don't care"
ctxt += tmp;
e = 2*e;
long b = bit(sz, j); // bit j of sz
// e -> e+b
if (b) {
ea.rotate1D(ctxt, d, 1, true); // "don't care"
ctxt += ctxt_orig;
e++;
}
}
}
}
// selects range of slots [lo..hi) in dimension d
static
void SelectRangeDim(const EncryptedArray& ea, ZZX& mask, long lo, long hi,
long d)
{
long nSlots = ea.size();
assert(d >= 0 && d < ea.dimension());
assert(lo >= 0 && lo <= hi && hi <= ea.sizeOfDimension(d));
vector<long> maskArray;
maskArray.resize(nSlots);
for (long i = 0; i < nSlots; i++) {
long c = ea.coordinate(d, i);
if (c >= lo && c < hi)
maskArray[i] = 1;
else
maskArray[i] = 0;
}
ea.encode(mask, maskArray);
}
void replicateAllNextDim(const EncryptedArray& ea, const Ctxt& ctxt,
long d, long dimProd, long recBound,
RepAuxDim& repAux, ReplicateHandler *handler)
{
assert(d >= 0);
// If already fully replicated (or we need to stop early), call the handler
if (d >= ea.dimension() || handler->earlyStop(d,/*k=*/-1,dimProd)) {
handler->handle(ctxt);
return;
}
long dSize = ea.sizeOfDimension(d);
dimProd *= dSize; // product of all dimensions including this one
long n = GreatestPowerOfTwo(dSize); // 2^n <= dSize
long k = n;
// We replicate 2^k-size blocks along this dimension, then call the
// recursive procedure to handle the smaller subblocks. Consider for
// example a 2D 5x2 cube, so the original slots are
//
// ( s0 s2 s4 s6 s8 )
// ( s1 s3 s5 s7 s9 )
//
// Say that we start with k=2 in the 1st dimension (of size 5), we
// will prepare floor(5/2)=2 ciphertexts as follows:
//
// ( s0 s2 s0 s2 0 ) ( s4 s6 s4 s6 0 )
// ( s1 s3 s1 s3 0 ) ( s5 s7 s5 s7 0 )
//
// The call to recursiveReplicateDim (still with k=2) will first copy
// s0/s1 and s4/s5 to the zero column at the end, then make a recursive
// call with k=1 that will complete the replication along the current
// dimension, resulting in the 4 ciphertexts
//
// (s0 s0 s0 s0 s0) (s2 s2 s2 s2 s2) (s4 s4 s4 s4 s4) (s6 s6 s6 s6 s6)
// (s1 s1 s1 s1 s1) (s3 s3 s3 s3 s3) (s5 s5 s5 s5 s5) (s7 s7 s7 s7 s7)
//
// Then a recursive call for the next dimension will complete the
// replication of these entries, and a final step will deal with the
// "leftover" positions s8 s9
// The logic below cut the recursion depth by starting from smaller
// blocks (by default size approx n rather than 2^n).
// The inital block size is controlled by the recBound parameter:
// + recBound>0: blocks of size min(~n, 2^recBound). this ensures
// recursion depth <= recBound, and typically much smaller (~log n)
// + recBound=0: blocks of size 1 (no recursion)
// + recBound<0: blocks of size 2^n (full recursion)
if (recBound >= 0) { // use heuristic recursion bound
k = 0;
if (dSize > 2 && dimProd*NumBits(dSize) > ea.size() / 8) {
k = NumBits(NumBits(dSize))-1;
if (k > n) k = n;
if (k > recBound) k = recBound;
}
}
else { // SHAI: I don't understand this else case
k = -recBound;
if (k > n) k = n;
}
long blockSize = 1L << k; // blocks of size 2^k
long numBlocks = dSize/blockSize;
long extent = numBlocks * blockSize;
// extent is an integral multiple of the block size, the recursive
// call replicates only these slots, and then we have a separate
// call for the leftover slots.
Ctxt ctxt1 = ctxt;
if (extent < dSize) { // select only the slots 0..extent-1 in this dimension
if (repAux.tab1(d, 0).null()) { // generate mask if not already there
ZZX mask;
SelectRangeDim(ea, mask, 0, extent, d);
repAux.tab1(d, 0).set_ptr(new DoubleCRT(mask, ea.getContext()));
// store mask in 2nd table (tab1)
}
ctxt1.multByConstant(*repAux.tab1(d, 0)); // mult by mask to zero out slots
}
if (numBlocks == 1) { // just one block, call the recursive replication
recursiveReplicateDim(ea, ctxt1, d, extent, k, 0, extent,
dimProd, recBound, repAux, handler);
}
else { // replicate the slots in each block separately
for (long pos = 0; pos < numBlocks; pos++) {
Ctxt ctxt2 = ctxt1;
// zero-out all the slots outside the current block
SelectRangeDim(ea, ctxt2, pos*blockSize, (pos+1)*blockSize, d);
// replicate the current block across this dimenssion using a
// simple shift-and-add procedure.
replicateOneBlock(ea, ctxt2, pos, blockSize, d);
// now call the recursive replication to do the rest of the work
recursiveReplicateDim(ea, ctxt2, d, extent, k, 0, extent,
dimProd, recBound, repAux, handler);
}
}
// If dSize is not an integral number of blocks, then we still need
// to deal with the leftover slots.
if (extent < dSize) {
// zero-out the slots from before, leaving only the leftover slots
ctxt1 = ctxt;
if (repAux.tab1(d, 1).null()) { // generate mask if not already there
ZZX mask;
SelectRangeDim(ea, mask, extent, dSize, d);
repAux.tab1(d, 1).set_ptr(new DoubleCRT(mask, ea.getContext()));
}
ctxt1.multByConstant(*repAux.tab1(d,1)); // mult by mask to zero out slots
// move relevant slots to the beginning
ea.rotate1D(ctxt1, d, -extent, /*don't-care-flag=*/true);
// replicate the leftover block across this dimenssion using a
// simple shift-and-add procedure.
replicateOneBlock(ea, ctxt1, 0, blockSize, d);
// now call the recursive replication to do the rest of the work
recursiveReplicateDim(ea, ctxt1, d, extent, k, extent, dSize,
dimProd, recBound, repAux, handler);
}
}
