malachite_nz/natural/conversion/
from_primitive_float.rs

1// Copyright © 2026 Mikhail Hogrefe
2//
3// This file is part of Malachite.
4//
5// Malachite is free software: you can redistribute it and/or modify it under the terms of the GNU
6// Lesser General Public License (LGPL) as published by the Free Software Foundation; either version
7// 3 of the License, or (at your option) any later version. See <https://www.gnu.org/licenses/>.
8
9use crate::natural::Natural;
10use core::cmp::Ordering::{self, *};
11use malachite_base::num::arithmetic::traits::ShlRound;
12use malachite_base::num::basic::traits::Zero;
13use malachite_base::num::conversion::from::UnsignedFromFloatError;
14use malachite_base::num::conversion::traits::{
15    ConvertibleFrom, IntegerMantissaAndExponent, IsInteger, RoundingFrom,
16};
17use malachite_base::rounding_modes::RoundingMode::{self, *};
18
19macro_rules! float_impls {
20    ($f: ident) => {
21        impl RoundingFrom<$f> for Natural {
22            /// Converts a floating-point value to a [`Natural`], using the specified rounding mode.
23            /// An [`Ordering`] is also returned, indicating whether the returned value is less
24            /// than, equal to, or greater than the original value.
25            ///
26            /// The floating-point value cannot be NaN or infinite, and it cannot round to a
27            /// negative integer.
28            ///
29            /// # Worst-case complexity
30            /// $T(n) = O(n)$
31            ///
32            /// $M(n) = O(n)$
33            ///
34            /// where $T$ is time, $M$ is additional memory, and $n$ is `value.sci_exponent()`.
35            ///
36            /// # Panics
37            /// Panics if `value` is NaN or infinite, if it would round to a negative integer, or if
38            /// the rounding mode is `Exact` and `value` is not an integer.
39            ///
40            /// # Examples
41            /// See [here](super::from_primitive_float#rounding_from).
42            fn rounding_from(value: $f, rm: RoundingMode) -> (Self, Ordering) {
43                if value.is_nan() || value == $f::INFINITY {
44                    panic!("Cannot convert {} to Natural", value);
45                } else if value == 0.0 {
46                    (Natural::ZERO, Equal)
47                } else if value < 0.0 {
48                    if rm == Down || rm == Ceiling || rm == Nearest {
49                        (Natural::ZERO, Greater)
50                    } else {
51                        panic!("Result is negative and cannot be converted to a Natural");
52                    }
53                } else {
54                    let (mantissa, exponent) = value.integer_mantissa_and_exponent();
55                    Natural::from(mantissa).shl_round(exponent, rm)
56                }
57            }
58        }
59
60        impl TryFrom<$f> for Natural {
61            type Error = UnsignedFromFloatError;
62
63            /// Converts a floating-point value to a [`Natural`].
64            ///
65            /// If the input isn't exactly equal to some [`Natural`], an error is returned.
66            ///
67            /// # Worst-case complexity
68            /// $T(n) = O(n)$
69            ///
70            /// $M(n) = O(n)$
71            ///
72            /// where $T$ is time, $M$ is additional memory, and $n$ is `value.sci_exponent()`.
73            ///
74            /// # Examples
75            /// See [here](super::from_primitive_float#try_from).
76            fn try_from(value: $f) -> Result<Natural, Self::Error> {
77                if value.is_nan() || value.is_infinite() {
78                    Err(UnsignedFromFloatError::FloatInfiniteOrNan)
79                } else if value < 0.0 {
80                    Err(UnsignedFromFloatError::FloatNegative)
81                } else if value == 0.0 {
82                    Ok(Natural::ZERO)
83                } else {
84                    let (mantissa, exponent) = value.integer_mantissa_and_exponent();
85                    if exponent >= 0 {
86                        Ok(Natural::from(mantissa) << exponent)
87                    } else {
88                        Err(UnsignedFromFloatError::FloatNonIntegerOrOutOfRange)
89                    }
90                }
91            }
92        }
93
94        impl ConvertibleFrom<$f> for Natural {
95            /// Determines whether a floating-point value can be exactly converted to a [`Natural`].
96            ///
97            /// # Worst-case complexity
98            /// Constant time and additional memory.
99            ///
100            /// # Examples
101            /// See [here](super::from_primitive_float#convertible_from).
102            #[inline]
103            fn convertible_from(value: $f) -> bool {
104                value >= 0.0 && value.is_integer()
105            }
106        }
107    };
108}
109apply_to_primitive_floats!(float_impls);
malachite_nz/natural/conversion/from_primitive_float.rs

malachite_nz/natural/conversion/
from_primitive_float.rs
