PC-1211, PC-1250, etc. TVM

[Albert Chan]

Plus42 uses NPMT formula and Newton's method for rate too.

Guess is picked so that each iteration, f always get better (closer to zero)
Termination criteria is that if f=0 or it change sign, or f not getting better.

Since ULP's are finite, even if f is at plateau, it always terminate.

https://raw.githubusercontent.com/thomas...mmands9.cc

Code:

if (p_isnan(f))
    return ERR_NO_SOLUTION_FOUND;
if (f == 0 || (f > 0) != (f0 > 0))
    break;
if (fabs(f) >= fabs(f0)) {
    if (i == i - eps / 1000) {
        i -= eps / 2;
        break;
    } else
        return ERR_NO_SOLUTION_FOUND;
}