add method
Adds the specified number to the adder’s current value.
Implementation
void add(double x) {
final p = _partials;
var i = 0;
for (var j = 0; j < _n && j < 32; j++) {
final y = p[j],
hi = x + y,
lo = x.abs() < y.abs() ? x - (hi - y) : y - (hi - x);
if (lo != 0) p[i++] = lo;
x = hi;
}
p[i] = x;
_n = i + 1;
}