1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154

//! Combines the Rust standard library's `NonZero` types into a single struct

use std::{
    fmt::Display,
    num::{NonZeroU128, NonZeroU16, NonZeroU32, NonZeroU64, NonZeroU8, NonZeroUsize},
    ops::Shr,
};

use num::{Integer, PrimInt};

/// Gives access to convenient methods for casting to `NonZero` or checking if you can.
pub trait NotZero: PrimInt + Integer {
    /// Shorthand for `!self.is_zero()`
    fn not_zero(self) -> bool {
        !self.is_zero()
    }

    /// Shorthand for `NonZero::new(self)`
    fn to_nonzero(self) -> Option<NonZero<Self>> {
        NonZero::new(self)
    }
}

impl<T> NotZero for T where T: PrimInt + Integer {}

/// An integer that is known to not equal zero.
#[derive(Debug, Copy, Clone, PartialOrd, Ord, PartialEq, Eq)]
pub struct NonZero<T: PrimInt + Integer> {
    value: T,
}

impl<T> Display for NonZero<T>
where
    T: PrimInt + Integer + Display,
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{}", self.value)
    }
}

impl<T> NonZero<T>
where
    T: PrimInt + Integer,
{
    /// Returns a new `NonZero<T>` if `value` is nonzero
    pub fn new(value: T) -> Option<Self> {
        value.not_zero().then_some(Self { value })
    }

    /// Returns a new `NonZero` without checking that the provided value is nonzero.
    /// # Safety
    /// `value` must be known to be nonzero
    pub const unsafe fn new_unchecked(value: T) -> Self {
        Self { value }
    }

    /// A copy of the nonzero value
    pub const fn get(self) -> T {
        self.value
    }

    /// Whether the nonzero integer is even
    pub fn is_even(self) -> bool {
        self.value.is_even()
    }

    /// Whether the nonzero integer is odd
    pub fn is_odd(self) -> bool {
        self.value.is_odd()
    }

    /// Sets `self.value` using the provided value.
    /// Only succeeds if the value provided was nonzero.
    /// Returns whether the operation succeeded.
    pub fn set(&mut self, value: T) -> bool {
        if value.not_zero() {
            unsafe { self.set_unchecked(value) }
        }
        value.not_zero()
    }

    /// Sets the internal value of the nonzero integer.
    /// If the value equals zero, this panics.
    /// # Safety
    /// `value` must be known to be nonzero
    pub unsafe fn set_unchecked(&mut self, value: T) {
        self.value = value;
    }

    /// Applies a function to the inner value and returns a `NonZero` if the result was nonzero.
    pub fn map(self, f: impl Fn(T) -> T) -> Option<Self> {
        Self::new(f(self.value))
    }

    /// Applies a function to the inner value and returns a `NonZero` if the result was nonzero.
    /// # Safety
    /// `f` must return a nonzero integer
    #[must_use]
    pub unsafe fn map_unchecked(self, f: fn(T) -> T) -> Self {
        Self::new_unchecked(f(self.value))
    }

    /// Returns the number of trailing zeros in the binary representation of the nonzero integer
    pub fn trailing_zeros(self) -> u32 {
        self.value.trailing_zeros()
    }
}

impl<T> NonZero<T>
where
    T: PrimInt + Integer + Shr<u32, Output = T>,
{
    /// Returns the number of trailing zeros in the binary representation of the nonzero integer
    #[must_use]
    pub fn without_trailing_zeros(self) -> Self {
        unsafe { Self::new_unchecked(self.value >> self.trailing_zeros()) }
    }
}

macro_rules! impl_from_primitive {
    ($new_name: ty, $primitive: ty) => {
        impl From<$primitive> for $new_name {
            fn from(value: $primitive) -> Self {
                Self { value: value.get() }
            }
        }
    };
}

impl_from_primitive!(NonZero<u8>, NonZeroU8);
impl_from_primitive!(NonZero<u16>, NonZeroU16);
impl_from_primitive!(NonZero<u32>, NonZeroU32);
impl_from_primitive!(NonZero<u64>, NonZeroU64);
impl_from_primitive!(NonZero<u128>, NonZeroU128);
impl_from_primitive!(NonZero<usize>, NonZeroUsize);

#[allow(unused_imports, clippy::unwrap_used)]
mod tests {
    use std::ops::Range;

    use num::{BigInt, FromPrimitive, One};

    use crate::NonZero;

    #[test]
    fn new_works() {
        assert!(NonZero::new(1u8).is_some());
        assert!(NonZero::new(1u16).is_some());
        assert!(NonZero::new(1u32).is_some());
        assert!(NonZero::new(1u64).is_some());
        assert!(NonZero::new(1u128).is_some());
        assert!(NonZero::new(1usize).is_some());
    }
}