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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::Float;
use core::cmp::Ordering::{self, *};
use malachite_base::num::basic::traits::{One, Two};
use malachite_base::rounding_modes::RoundingMode::{self, *};
impl Float {
/// Returns an approximation of the golden ratio, with the given precision and rounded using the
/// given [`RoundingMode`]. An [`Ordering`] is also returned, indicating whether the rounded
/// value is less than or greater than the exact value of the constant. (Since the constant is
/// irrational, the rounded value is never equal to the exact value.)
///
/// $$
/// \varphi = \frac{1+\sqrt{2}}{2}+\varepsilon.
/// $$
/// - If $m$ is not `Nearest`, then $|\varepsilon| < 2^{-p}$.
/// - If $m$ is `Nearest`, then $|\varepsilon| < 2^{-p-1}$.
///
/// The constant is irrational and algebraic.
///
/// The output has precision `prec`.
///
/// # Worst-case complexity
/// $T(n) = O(n \log n \log\log n)$
///
/// $M(n) = O(n \log n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `prec`.
///
/// # Panics
/// Panics if `prec` is zero or if `rm` is `Exact`.
///
/// # Examples
/// ```
/// use malachite_base::rounding_modes::RoundingMode::*;
/// use malachite_float::Float;
/// use std::cmp::Ordering::*;
///
/// let (phi, o) = Float::phi_prec_round(100, Floor);
/// assert_eq!(phi.to_string(), "1.618033988749894848204586834364");
/// assert_eq!(o, Less);
///
/// let (phi, o) = Float::phi_prec_round(100, Ceiling);
/// assert_eq!(phi.to_string(), "1.618033988749894848204586834366");
/// assert_eq!(o, Greater);
/// ```
#[inline]
pub fn phi_prec_round(prec: u64, rm: RoundingMode) -> (Self, Ordering) {
if prec == 1 {
match rm {
Floor | Down => (Self::ONE, Less),
Ceiling | Up | Nearest => (Self::TWO, Greater),
Exact => panic!("Inexact float square root"),
}
} else {
let (sqrt_5, o) =
Self::sqrt_prec_round(const { Self::const_from_unsigned(5) }, prec, rm);
((sqrt_5 + Self::ONE) >> 1u32, o)
}
}
/// Returns an approximation of the golden ratio, with the given precision and rounded to the
/// nearest [`Float`] of that precision. An [`Ordering`] is also returned, indicating whether
/// the rounded value is less than or greater than the exact value of the constant. (Since the
/// constant is irrational, the rounded value is never equal to the exact value.)
///
/// $$
/// \varphi = \frac{1+\sqrt{2}}{2}+\varepsilon.
/// $$
/// - $|\varepsilon| < 2^{-p}$.
///
/// The constant is irrational and algebraic.
///
/// The output has precision `prec`.
///
/// # Worst-case complexity
/// $T(n) = O(n \log n \log\log n)$
///
/// $M(n) = O(n \log n)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `prec`.
///
/// # Panics
/// Panics if `prec` is zero.
///
/// # Examples
/// ```
/// use malachite_float::Float;
/// use std::cmp::Ordering::*;
///
/// let (phi, o) = Float::phi_prec(1);
/// assert_eq!(phi.to_string(), "2.0");
/// assert_eq!(o, Greater);
///
/// let (phi, o) = Float::phi_prec(10);
/// assert_eq!(phi.to_string(), "1.617");
/// assert_eq!(o, Less);
///
/// let (phi, o) = Float::phi_prec(100);
/// assert_eq!(phi.to_string(), "1.618033988749894848204586834366");
/// assert_eq!(o, Greater);
/// ```
#[inline]
pub fn phi_prec(prec: u64) -> (Self, Ordering) {
Self::phi_prec_round(prec, Nearest)
}
}