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use crate::{
abs_diff::abs_diff,
greatest_common_divisor_euclidean::gcd,
};
/// n is not prime.
/// if prime, check in advance with primality test like miller-rabin.
/// return divisor of n. (1 < d < n)
pub fn find_divisor_pollard_rho_floyd<F>(
n: u64,
prng_next: &F,
) -> Result<u64, &'static str>
where
F: Fn(u64) -> u64,
{
assert!(n > 2);
let (mut x, mut y, mut d) = (2, 2, 1);
while d == 1 {
x = prng_next(x);
y = prng_next(prng_next(y));
d = gcd(abs_diff(x, y), n);
}
if d == n {
Err("No divisor found")
} else {
Ok(d)
}
}
// TODO:
#[cfg(test)]
mod tests {
#[test]
fn test() {}
}