Move find_intermediate to the server crate

[uonr]

https://wiki.postgresql.org/wiki/User-specified_ordering_with_fractions

Translate by Claude

use std::cmp::Ordering;

/// Find an intermediate fraction between p1/q1 and p2/q2.
///
/// The fraction chosen is the highest fraction in the Stern-Brocot
/// tree which falls strictly between the specified values.
///
/// Inputs must not be null (caller's responsibility), but the value
/// p2=1 q2=0 is allowed for the upper bound without causing any
/// division by zero errors.
fn find_intermediate(p1: i32, q1: i32, p2: i32, q2: i32) -> (i32, i32) {
    let mut pl = 0;
    let mut ql = 1;
    let mut ph = 1;
    let mut qh = 0;

    if (p1 as i64 * q2 as i64 + 1) != (p2 as i64 * q1 as i64) {
        loop {
            let p = pl + ph;
            let q = ql + qh;

            match ((p as i64 * q1 as i64).cmp(&(q as i64 * p1 as i64)), 
                   (p2 as i64 * q as i64).cmp(&(q2 as i64 * p as i64))) {
                (Ordering::Less | Ordering::Equal, _) => {
                    pl = p;
                    ql = q;
                }
                (_, Ordering::Less | Ordering::Equal) => {
                    ph = p;
                    qh = q;
                }
                _ => return (p, q),
            }
        }
    } else {
        (p1 + p2, q1 + q2)
    }
}

fn main() {
    let (p, q) = find_intermediate(1, 3, 2, 5);
    println!("Intermediate fraction: {}/{}", p, q);
}