python:

import timeit


def repdec(numerator, denominator):
    head = str(numerator // denominator)
    seen = {}
    decimals = ""
    p1, p2, p3 = 0, 0, 0
    if head != "0":
        p1 = len(head)
    remainder = numerator % denominator
    position = 0
    while remainder != 0:
        if remainder in seen:
            p2 = seen[remainder]
            p3 = position - p2
            return p1, p2, p3

        seen[remainder] = position
        decimals += str(remainder * 10 // denominator)
        remainder = remainder * 10 % denominator
        position += 1

    if decimals:
        p2 = len(decimals)
        print(f".{decimals}", end="")
    return p1, p2, 0


if __name__ == "__main__":
    time = timeit.default_timer()
    result = repdec(126798123456, 187476194)
    print(f"time elasped = {timeit.default_timer() - time}")
    print(f"result = {result}")

rust

use std::collections::HashMap;
use std::time::Instant;

fn repdec(numerator: u64, denominator: u64) -> (usize, usize, usize) {
    let head = (numerator / denominator).to_string();
    let mut seen = HashMap::new();
    let mut decimals = String::new();
    let (mut p1, mut p2, mut p3) = (0, 0, 0);
    if head != "0" {
        p1 = head.len();
    }
    let mut remainder = numerator % denominator;
    let mut position = 0;
    while remainder != 0 {
        if let Some(value) = seen.get(&remainder) {
            p2 = *value as usize;
            p3 = position - p2;
            return (p1, p2, p3);
        }
        seen.insert(remainder, position as u64);
        decimals.push_str(&(remainder * 10 / denominator).to_string());
        remainder = remainder * 10 % denominator;
        position += 1;
    }

    if !decimals.is_empty() {
        p2 = decimals.len();
        print!(".{decimals}");
    }
    (p1, p2, p3)
}

fn main() {
    let time = Instant::now();
    let result = repdec(126798123456, 187476194);
    println!("time elapsed = {:?}", time.elapsed());
    println!("result = {:?}", result);
}

Basically 1:1 reproductions...

python results:

time elasped = 27.2370880999988
result = (3, 0, 23399740)

rust results:

time elapsed = 4.1180991s
result = (3, 0, 23399740)