C++ ZZX::SetMaxLength方法代码示例

void sampleGaussian(ZZX &poly, long n, double stdev)
{
  static double const Pi=4.0*atan(1.0); // Pi=3.1415..
  static long const bignum = 0xfffffff;
  // THREADS: C++11 guarantees these are initialized only once

  if (n<=0) n=deg(poly)+1; if (n<=0) return;
  poly.SetMaxLength(n); // allocate space for degree-(n-1) polynomial
  for (long i=0; i<n; i++) SetCoeff(poly, i, ZZ::zero());

  // Uses the Box-Muller method to get two Normal(0,stdev^2) variables
  for (long i=0; i<n; i+=2) {
    double r1 = (1+RandomBnd(bignum))/((double)bignum+1);
    double r2 = (1+RandomBnd(bignum))/((double)bignum+1);
    double theta=2*Pi*r1;
    double rr= sqrt(-2.0*log(r2))*stdev;

    assert(rr < 8*stdev); // sanity-check, no more than 8 standard deviations

    // Generate two Gaussians RV's, rounded to integers
    long x = (long) floor(rr*cos(theta) +0.5);
    SetCoeff(poly, i, x);
    if (i+1 < n) {
      x = (long) floor(rr*sin(theta) +0.5);
      SetCoeff(poly, i+1, x);
    }
  }
  poly.normalize(); // need to call this after we work on the coeffs
}

ZZX RandPoly(long n,const ZZ& p)
{ 
  ZZX F; F.SetMaxLength(n);
  ZZ p2;  p2=p>>1;
  for (long i=0; i<n; i++)
    { SetCoeff(F,i,RandomBnd(p)-p2); }
  return F;
}

// multiply the polynomial f by the integer a modulo q
void MulMod(ZZX& out, const ZZX& f, long a, long q, bool abs/*default=true*/)
{
  // ensure that out has the same degree as f
  out.SetMaxLength(deg(f)+1);               // allocate space if needed
  if (deg(out)>deg(f)) trunc(out,out,deg(f)+1); // remove high degrees

  for (int i=0; i<=deg(f); i++) { 
    int c = rem(coeff(f,i), q);
    c = MulMod(c, a, q); // returns c \in [0,q-1]
    if (!abs && c >= q/2)
      c -= q;
    SetCoeff(out,i,c);
  }
}

void sampleSmall(ZZX &poly, long n)
{
  if (n<=0) n=deg(poly)+1; if (n<=0) return;
  poly.SetMaxLength(n); // allocate space for degree-(n-1) polynomial

  for (long i=0; i<n; i++) {    // Chosse coefficients, one by one
    long u = lrand48();
    if (u&1) {                 // with prob. 1/2 choose between -1 and +1
      u = (u & 2) -1;
      SetCoeff(poly, i, u);
    }
    else SetCoeff(poly, i, 0); // with ptob. 1/2 set to 0
  }
  poly.normalize(); // need to call this after we work on the coeffs
}

void sampleHWt(ZZX &poly, long Hwt, long n)
{
  if (n<=0) n=deg(poly)+1; if (n<=0) return;
  clear(poly);          // initialize to zero
  poly.SetMaxLength(n); // allocate space for degree-(n-1) polynomial

  long b,u,i=0;
  if (Hwt>n) Hwt=n;
  while (i<Hwt) {  // continue until exactly Hwt nonzero coefficients
    u=lrand48()%n; // The next coefficient to choose
    if (IsZero(coeff(poly,u))) { // if we didn't choose it already
      b = lrand48()&2; // b random in {0,2}
      b--;             //   random in {-1,1}
      SetCoeff(poly,u,b);

      i++; // count another nonzero coefficient
    }
  }
  poly.normalize(); // need to call this after we work on the coeffs
}

void PolyRed(ZZX& out, const ZZX& in, long q, bool abs)
{
  // ensure that out has the same degree as in
  out.SetMaxLength(deg(in)+1);               // allocate space if needed
  if (deg(out)>deg(in)) trunc(out,out,deg(in)+1); // remove high degrees

  long q2; q2=q>>1;
  for (long i=0; i<=deg(in); i++)
    { long c=coeff(in,i)%q;
      if (abs)
        { if (c<0) { c=c+q; } }
      else if (q==2)
        { if (coeff(in,i)<0) { c=-c; } }
      else
        { if (c>=q2)  { c=c-q; }
          else if (c<-q2) { c=c+q; }
	}
      SetCoeff(out,i,c);
    }
}

void sampleUniform(ZZX& poly, const ZZ& B, long n)
{
  if (n<=0) n=deg(poly)+1; if (n<=0) return;
  if (B <= 0) {
    clear(poly);
    return;
  }

  poly.SetMaxLength(n); // allocate space for degree-(n-1) polynomial

  ZZ UB, tmp;

  UB =  2*B + 1;
  for (long i = 0; i < n; i++) {
    RandomBnd(tmp, UB);
    tmp -= B; 
    poly.rep[i] = tmp;
  }

  poly.normalize();
}