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// Copyright © 2026 Mikhail Hogrefe
//
// This file is part of Malachite.
//
// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
use crate::Rational;
use core::cmp::Ordering::*;
use malachite_base::num::arithmetic::traits::{
CeilingLogBase2, CeilingLogBasePowerOf2, CheckedLogBase2, CheckedLogBasePowerOf2, DivMod,
DivRound, FloorLogBase2, FloorLogBasePowerOf2, Sign,
};
use malachite_base::rounding_modes::RoundingMode::*;
impl FloorLogBasePowerOf2<i64> for &Rational {
type Output = i64;
/// Returns the floor of the base-$2^k$ logarithm of a positive [`Rational`].
///
/// $k$ may be negative.
///
/// $f(x, k) = \lfloor\log_{2^k} x\rfloor$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.significant_bits()`.
///
/// # Panics
/// Panics if `self` is less than or equal to 0 or `pow` is 0.
///
/// # Examples
/// ```
/// use malachite_base::num::arithmetic::traits::FloorLogBasePowerOf2;
/// use malachite_q::Rational;
///
/// assert_eq!(Rational::from(100).floor_log_base_power_of_2(2), 3);
/// assert_eq!(
/// Rational::from(4294967296u64).floor_log_base_power_of_2(8),
/// 4
/// );
///
/// // 4^(-2) < 1/10 < 4^(-1)
/// assert_eq!(
/// Rational::from_signeds(1, 10).floor_log_base_power_of_2(2),
/// -2
/// );
/// // (1/4)^2 < 1/10 < (1/4)^1
/// assert_eq!(
/// Rational::from_signeds(1, 10).floor_log_base_power_of_2(-2),
/// 1
/// );
/// ```
fn floor_log_base_power_of_2(self, pow: i64) -> i64 {
assert!(*self > 0u32);
match pow.sign() {
Equal => panic!("Cannot take base-1 logarithm"),
Greater => self.floor_log_base_2().div_round(pow, Floor).0,
Less => -(self.ceiling_log_base_2().div_round(-pow, Ceiling).0),
}
}
}
impl CeilingLogBasePowerOf2<i64> for &Rational {
type Output = i64;
/// Returns the ceiling of the base-$2^k$ logarithm of a positive [`Rational`].
///
/// $k$ may be negative.
///
/// $f(x, p) = \lceil\log_{2^p} x\rceil$.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.significant_bits()`.
///
/// # Panics
/// Panics if `self` is less than or equal to 0 or `pow` is 0.
///
/// # Examples
/// ```
/// use malachite_base::num::arithmetic::traits::CeilingLogBasePowerOf2;
/// use malachite_q::Rational;
///
/// assert_eq!(Rational::from(100).ceiling_log_base_power_of_2(2), 4);
/// assert_eq!(
/// Rational::from(4294967296u64).ceiling_log_base_power_of_2(8),
/// 4
/// );
///
/// // 4^(-2) < 1/10 < 4^(-1)
/// assert_eq!(
/// Rational::from_signeds(1, 10).ceiling_log_base_power_of_2(2),
/// -1
/// );
/// // (1/4)^2 < 1/10 < (1/4)^1
/// assert_eq!(
/// Rational::from_signeds(1, 10).ceiling_log_base_power_of_2(-2),
/// 2
/// );
/// ```
fn ceiling_log_base_power_of_2(self, pow: i64) -> i64 {
assert!(*self > 0u32);
match pow.sign() {
Equal => panic!("Cannot take base-1 logarithm"),
Greater => self.ceiling_log_base_2().div_round(pow, Ceiling).0,
Less => -self.floor_log_base_2().div_round(-pow, Floor).0,
}
}
}
impl CheckedLogBasePowerOf2<i64> for &Rational {
type Output = i64;
/// Returns the base-$2^k$ logarithm of a positive [`Rational`]. If the [`Rational`] is not a
/// power of $2^k$, then `None` is returned.
///
/// $k$ may be negative.
///
/// $$
/// f(x, p) = \\begin{cases}
/// \operatorname{Some}(\log_{2^p} x) & \text{if} \\quad \log_{2^p} x \in \Z, \\\\
/// \operatorname{None} & \textrm{otherwise}.
/// \\end{cases}
/// $$
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `self.significant_bits()`.
///
/// # Panics
/// Panics if `self` is 0 or `pow` is 0.
///
/// # Examples
/// ```
/// use malachite_base::num::arithmetic::traits::CheckedLogBasePowerOf2;
/// use malachite_q::Rational;
///
/// assert_eq!(Rational::from(100).checked_log_base_power_of_2(2), None);
/// assert_eq!(
/// Rational::from(4294967296u64).checked_log_base_power_of_2(8),
/// Some(4)
/// );
///
/// // 4^(-2) < 1/10 < 4^(-1)
/// assert_eq!(
/// Rational::from_signeds(1, 10).checked_log_base_power_of_2(2),
/// None
/// );
/// assert_eq!(
/// Rational::from_signeds(1, 16).checked_log_base_power_of_2(2),
/// Some(-2)
/// );
/// // (1/4)^2 < 1/10 < (1/4)^1
/// assert_eq!(
/// Rational::from_signeds(1, 10).checked_log_base_power_of_2(-2),
/// None
/// );
/// assert_eq!(
/// Rational::from_signeds(1, 16).checked_log_base_power_of_2(-2),
/// Some(2)
/// );
/// ```
fn checked_log_base_power_of_2(self, pow: i64) -> Option<i64> {
assert!(*self > 0u32);
let log_base_2 = self.checked_log_base_2()?;
let (pow, neg) = match pow.sign() {
Equal => panic!("Cannot take base-1 logarithm"),
Greater => (pow, false),
Less => (-pow, true),
};
let (log, rem) = log_base_2.div_mod(pow);
if rem != 0 {
None
} else if neg {
Some(-log)
} else {
Some(log)
}
}
}