Summator.opOpAssign

import mir.math.common;
import mir.ndslice.topology: iota, map;
auto r1 = iota(500).map!(a => 1.7L.pow(a+1) - 1.7L.pow(a));
auto r2 = iota([500], 500).map!(a => 1.7L.pow(a+1) - 1.7L.pow(a));
Summator!(real, Summation.precise) s1 = 0, s2 = 0.0;
foreach (e; r1) s1 += e;
foreach (e; r2) s2 -= e;
s1 -= s2;
s1 -= 1.7L.pow(1000);
assert(s1.sum == -1);