Kahan summation algorithm

The Kahan summation algorithm, also known as compensated summation, is a numerical technique used to improve the precision of the summation of a sequence of floating-point numbers. It mitigates the error that can occur when small numbers are added to large numbers, a common issue in floating-point arithmetic due to limited precision. ### How it Works The algorithm maintains an extra variable (often called `c`, for "compensation") that keeps track of small error terms.