static
void LocalCopyReverse(zz_pX& x, const zz_pX& a, long lo, long hi)
// x[0..hi-lo] = reverse(a[lo..hi]), with zero fill
// input may not alias output
{
long i, j, n, m;
n = hi-lo+1;
m = a.rep.length();
x.rep.SetLength(n);
const zz_p* ap = a.rep.elts();
zz_p* xp = x.rep.elts();
for (i = 0; i < n; i++) {
j = hi-i;
if (j < 0 || j >= m)
clear(xp[i]);
else
xp[i] = ap[j];
}
x.normalize();
}
static
void LocalCyclicReduce(zz_pX& x, const zz_pX& a, long m)
// computes x = a mod X^m-1
{
long n = deg(a);
long i, j;
zz_p accum;
if (n < m) {
x = a;
return;
}
if (&x != &a)
x.rep.SetLength(m);
for (i = 0; i < m; i++) {
accum = a.rep[i];
for (j = i + m; j <= n; j += m)
add(accum, accum, a.rep[j]);
x.rep[i] = accum;
}
if (&x == &a)
x.rep.SetLength(m);
x.normalize();
}
void diff(zz_pX& x, const zz_pX& a)
{
long n = deg(a);
long i;
if (n <= 0) {
clear(x);
return;
}
if (&x != &a)
x.rep.SetLength(n);
for (i = 0; i <= n-1; i++) {
mul(x.rep[i], a.rep[i+1], i+1);
}
if (&x == &a)
x.rep.SetLength(n);
x.normalize();
}
void ShiftSub(zz_pX& U, const zz_pX& V, long n)
// assumes input does not alias output
{
if (IsZero(V))
return;
long du = deg(U);
long dv = deg(V);
long d = max(du, n+dv);
U.rep.SetLength(d+1);
long i;
for (i = du+1; i <= d; i++)
clear(U.rep[i]);
for (i = 0; i <= dv; i++)
sub(U.rep[i+n], U.rep[i+n], V.rep[i]);
U.normalize();
}
// This routine recursively reduces each hypercolumn
// in dimension d (viewed as a coeff vector) by Phi_{m_d}(X)
// If one starts with a cube of dimension (m_1, ..., m_k),
// one ends up with a cube that is effectively of dimension
// phi(m_1, ..., m_k). Viewed as an element of the ring
// F_p[X_1,...,X_k]/(Phi_{m_1}(X_1), ..., Phi_{m_k}(X_k)),
// the cube remains unchanged.
static void recursiveReduce(const CubeSlice<zz_p>& s,
const Vec<zz_pXModulus>& cycVec,
long d,
zz_pX& tmp1,
zz_pX& tmp2)
{
long numDims = s.getNumDims();
//OLD: assert(numDims > 0);
helib::assertTrue(numDims > 0l, "CubeSlice s has negative number of dimensions");
long deg0 = deg(cycVec[d]);
long posBnd = s.getProd(1);
for (long pos = 0; pos < posBnd; pos++) {
getHyperColumn(tmp1.rep, s, pos);
tmp1.normalize();
// tmp2 may not be normalized, so clear it first
clear(tmp2);
rem(tmp2, tmp1, cycVec[d]);
// now pad tmp2.rep with zeros to length deg0...
// tmp2 may not be normalized
long len = tmp2.rep.length();
tmp2.rep.SetLength(deg0);
for (long i = len; i < deg0; i++) tmp2.rep[i] = 0;
setHyperColumn(tmp2.rep, s, pos);
}
if (numDims == 1) return;
for (long i = 0; i < deg0; i++)
recursiveReduce(CubeSlice<zz_p>(s, i), cycVec, d+1, tmp1, tmp2);
}
void BluesteinInit(long n, const zz_p& root, zz_pX& powers,
Vec<mulmod_precon_t>& powers_aux, fftRep& Rb)
{
long p = zz_p::modulus();
zz_p one; one=1;
powers.SetMaxLength(n);
SetCoeff(powers,0,one);
for (long i=1; i<n; i++) {
long iSqr = MulMod(i, i, 2*n); // i^2 mod 2n
SetCoeff(powers,i, power(root,iSqr)); // powers[i] = root^{i^2}
}
// powers_aux tracks powers
powers_aux.SetLength(n);
for (long i = 0; i < n; i++)
powers_aux[i] = PrepMulModPrecon(rep(powers[i]), p);
long k = NextPowerOfTwo(2*n-1);
long k2 = 1L << k; // k2 = 2^k
Rb.SetSize(k);
zz_pX b(INIT_SIZE, k2);
zz_p rInv = inv(root);
SetCoeff(b,n-1,one); // b[n-1] = 1
for (long i=1; i<n; i++) {
long iSqr = MulMod(i, i, 2*n); // i^2 mod 2n
zz_p bi = power(rInv,iSqr);
SetCoeff(b,n-1+i, bi); // b[n-1+i] = b[n-1-i] = root^{-i^2}
SetCoeff(b,n-1-i,bi);
}
TofftRep(Rb, b, k);
}
void recursiveEval(const CubeSlice<zz_p>& s,
const Vec< copied_ptr<FFTHelper> >& multiEvalPoints,
long d,
zz_pX& tmp1,
Vec<zz_p>& tmp2)
{
long numDims = s.getNumDims();
assert(numDims > 0);
if (numDims > 1) {
long dim0 = s.getDim(0);
for (long i = 0; i < dim0; i++)
recursiveEval(CubeSlice<zz_p>(s, i), multiEvalPoints, d+1, tmp1, tmp2);
}
long posBnd = s.getProd(1);
for (long pos = 0; pos < posBnd; pos++) {
getHyperColumn(tmp1.rep, s, pos);
tmp1.normalize();
multiEvalPoints[d]->FFT(tmp1, tmp2);
setHyperColumn(tmp2, s, pos);
}
}
void Cmodulus::iFFT(zz_pX &x, const vec_long& y)const
{
FHE_TIMER_START;
zz_pBak bak; bak.save();
context.restore();
if (zMStar->getPow2()) {
// special case when m is a power of 2
long k = zMStar->getPow2();
long phim = (1L << (k-1));
long p = zz_p::modulus();
const zz_p *ipowers_p = (*ipowers).rep.elts();
const mulmod_precon_t *ipowers_aux_p = ipowers_aux.elts();
const long *yp = y.elts();
vec_long& tmp = Cmodulus::getScratch_vec_long();
tmp.SetLength(phim);
long *tmp_p = tmp.elts();
#ifdef FHE_OPENCL
AltFFTRev1(tmp_p, yp, k-1, *altFFTInfo);
#else
FFTRev1(tmp_p, yp, k-1, *zz_pInfo->p_info);
#endif
x.rep.SetLength(phim);
zz_p *xp = x.rep.elts();
for (long i = 0; i < phim; i++)
xp[i].LoopHole() = MulModPrecon(tmp_p[i], rep(ipowers_p[i]), p, ipowers_aux_p[i]);
x.normalize();
return;
}
zz_p rt;
long m = getM();
// convert input to zpx format, initializing only the coeffs i s.t. (i,m)=1
x.rep.SetLength(m);
long i,j;
for (i=j=0; i<m; i++)
if (zMStar->inZmStar(i)) x.rep[i].LoopHole() = y[j++]; // DIRT: y[j] already reduced
x.normalize();
conv(rt, rInv); // convert rInv to zp format
BluesteinFFT(x, m, rt, *ipowers, ipowers_aux, *iRb); // call the FFT routine
// reduce the result mod (Phi_m(X),q) and copy to the output polynomial x
{ FHE_NTIMER_START(iFFT_division);
rem(x, x, *phimx); // out %= (Phi_m(X),q)
}
// normalize
zz_p mm_inv;
conv(mm_inv, m_inv);
x *= mm_inv;
}
