Function pos_search 

pub fn pos_search(x: f64, xs: &[f64]) -> usize

Finds the position for interpolation in a sorted array.

Returns the index of the largest element in xs that is less than x, clamped to the valid range [0, xs.len() - 1].

Edge Cases

• For empty arrays, returns 0
• For single-element arrays, always returns index 0, regardless of whether x > xs[0]
• For values below the minimum, returns 0
• For values at or above the maximum, returns xs.len() - 1

Examples

use nautilus_core::math::pos_search;

// Normal case: find position between elements
assert_eq!(pos_search(2.5, &[1.0, 2.0, 3.0, 4.0]), 1); // Between indices 1 and 2

// Single element: always returns 0
assert_eq!(pos_search(5.0, &[10.0]), 0); // Even though x < xs[0]
assert_eq!(pos_search(15.0, &[10.0]), 0); // Even though x > xs[0]