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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::natural::Natural;
use core::cmp::Ordering::{self, *};
use malachite_base::named::Named;
use malachite_base::num::arithmetic::traits::DivisibleByPowerOf2;
use malachite_base::num::basic::floats::PrimitiveFloat;
use malachite_base::num::conversion::traits::{
ConvertibleFrom, ExactFrom, RawMantissaAndExponent, RoundingFrom, SciMantissaAndExponent,
WrappingFrom,
};
use malachite_base::rounding_modes::RoundingMode::{self, *};
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub struct PrimitiveFloatFromNaturalError;
macro_rules! float_impls {
($f: ident) => {
impl<'a> RoundingFrom<&'a Natural> for $f {
/// Converts a [`Natural`] to a primitive float according to a specified
/// [`RoundingMode`]. An [`Ordering`] is also returned, indicating whether the returned
/// value is less than, equal to, or greater than the original value.
///
/// - If the rounding mode is `Floor` or `Down`, the largest float less than or equal to
/// the [`Natural`] is returned. If the [`Natural`] is greater than the maximum finite
/// float, then the maximum finite float is returned.
/// - If the rounding mode is `Ceiling` or `Up`, the smallest float greater than or
/// equal to the [`Natural`] is returned. If the [`Natural`] is greater than the
/// maximum finite float, then $\infty$ is returned.
/// - If the rounding mode is `Nearest`, then the nearest float is returned. If the
/// [`Natural`] is exactly between two floats, the float with the zero
/// least-significant bit in its representation is selected. If the [`Natural`] is
/// greater than the maximum finite float, then $\infty$ is returned.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `value.significant_bits()`.
///
/// # Panics
/// Panics if the rounding mode is `Exact` and `value` cannot be represented exactly.
///
/// # Examples
/// See [here](super::primitive_float_from_natural#rounding_from).
fn rounding_from(value: &'a Natural, rm: RoundingMode) -> ($f, Ordering) {
if *value == 0 {
(0.0, Equal)
} else {
let (mantissa, exponent, o) = value
.sci_mantissa_and_exponent_round(rm)
.expect("Value cannot be represented exactly as a float");
if let Some(f) =
$f::from_sci_mantissa_and_exponent(mantissa, i64::exact_from(exponent))
{
(f, o)
} else {
match rm {
Exact => {
panic!("Value cannot be represented exactly as an {}", $f::NAME)
}
Floor | Down => ($f::MAX_FINITE, Less),
_ => ($f::INFINITY, Greater),
}
}
}
}
}
impl<'a> TryFrom<&'a Natural> for $f {
type Error = PrimitiveFloatFromNaturalError;
/// Converts a [`Natural`] to a primitive float.
///
/// If the input isn't exactly equal to some float, an error is returned.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `value.significant_bits()`.
///
/// # Examples
/// See [here](super::primitive_float_from_natural#try_from).
fn try_from(value: &'a Natural) -> Result<$f, Self::Error> {
if *value == 0 {
Ok(0.0)
} else {
let (mantissa, exponent, _) = value
.sci_mantissa_and_exponent_round(Exact)
.ok_or(PrimitiveFloatFromNaturalError)?;
$f::from_sci_mantissa_and_exponent(mantissa, i64::exact_from(exponent))
.ok_or(PrimitiveFloatFromNaturalError)
}
}
}
impl<'a> ConvertibleFrom<&'a Natural> for $f {
/// Determines whether a [`Natural`] can be exactly converted to a primitive float.
///
/// # Worst-case complexity
/// $T(n) = O(n)$
///
/// $M(n) = O(1)$
///
/// where $T$ is time, $M$ is additional memory, and $n$ is `value.significant_bits()`.
///
/// # Examples
/// See [here](super::primitive_float_from_natural#convertible_from).
fn convertible_from(value: &'a Natural) -> bool {
if *value == 0 {
true
} else {
if let Some((mantissa, exponent, _)) =
value.sci_mantissa_and_exponent_round::<$f>(Exact)
{
let exponent = i64::exact_from(exponent);
if !($f::MIN_EXPONENT..=$f::MAX_EXPONENT).contains(&exponent) {
return false;
}
let (orig_mantissa, orig_exponent) = mantissa.raw_mantissa_and_exponent();
orig_exponent == u64::wrapping_from($f::MAX_EXPONENT)
&& exponent >= $f::MIN_NORMAL_EXPONENT
|| orig_mantissa.divisible_by_power_of_2(u64::wrapping_from(
$f::MIN_NORMAL_EXPONENT - exponent,
))
} else {
false
}
}
}
}
};
}
apply_to_primitive_floats!(float_impls);