Method SetupField

secp256k1/IntMod.cpp:685–733

// ------------------------------------------------

void Int::SetupField(Int *n, Int *R, Int *R2, Int *R3, Int *R4) {

  // Size in number of 32bit word
  int nSize = n->GetSize();

  // Last digit inversions (Newton's iteration)
  {
    int64_t x, t;
    x = t = (int64_t)n->bits64[0];
    x = x * (2 - t * x);
    x = x * (2 - t * x);
    x = x * (2 - t * x);
    x = x * (2 - t * x);
    x = x * (2 - t * x);
    MM64 = (uint64_t)(-x);
    MM32 = (uint32_t)MM64;
  }
  _P.Set(n);

  // Size of Montgomery mult (64bits digit)
  Msize = nSize/2;

  // Compute few power of R
  // R = 2^(64*Msize) mod n
  Int Ri;
  Ri.MontgomeryMult(&_ONE, &_ONE); // Ri = R^-1
  _R.Set(&Ri);                     // R  = R^-1
  _R2.MontgomeryMult(&Ri, &_ONE);  // R2 = R^-2
  _R3.MontgomeryMult(&Ri, &Ri);    // R3 = R^-3
  _R4.MontgomeryMult(&_R3, &_ONE); // R4 = R^-4

  _R.ModInv();                     // R  = R
  _R2.ModInv();                    // R2 = R^2
  _R3.ModInv();                    // R3 = R^3
  _R4.ModInv();                    // R4 = R^4

  if (R)
    R->Set(&_R);

  if (R2)
    R2->Set(&_R2);

  if (R3)
    R3->Set(&_R3);

  if (R4)
    R4->Set(&_R4);

}
// ------------------------------------------------

uint64_t Int::AddC(Int *a) {