Function discounted_sum 

pub fn discounted_sum<R: Scalar>(
    flows: &[Cashflow<R>],
    disc: &dyn YieldCurve<R>,
) -> Result<R, CurveError>

The sum of flows discounted on disc — the shared NPV kernel.

Two passes and one fused product: the first pass evaluates each discount factor (recording whatever the curve’s interpolation records), and Real::dot then closes the accumulation as a single n-ary statement rather than a 2n-long multiply-add chain. The passive mode takes the same shape and gets a plain vectorizable loop out of it.

An empty set of flows is zero.

Errors

Whatever the curve reports — CurveError::BeforeReference if a payment falls before the curve’s own anchor.