Method ModInv

IntGroup.cpp:36–58

Compute modular inversion of the whole group

// Compute modular inversion of the whole group
void IntGroup::ModInv() {

  Int newValue;
  Int inverse;

  subp[0].Set(&ints[0]);
  for (int i = 1; i < size; i++) {
    subp[i].ModMulK1(&subp[i - 1], &ints[i]);
  }

  // Do the inversion
  inverse.Set(&subp[size - 1]);
  inverse.ModInv();

  for (int i = size - 1; i > 0; i--) {
    newValue.ModMulK1(&subp[i - 1], &inverse);
    inverse.ModMulK1(&ints[i]);
    ints[i].Set(&newValue);
  }

  ints[0].Set(&inverse);

}