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
155
156
157
158
159
160
161
162
163
164
165

//! Utilities for const contexts.

use crate::std_types::RStr;

pub use abi_stable_shared::const_utils::low_bit_mask_u64;

//////////////////////////////////////////////////////////////////

// Used to test trait bounds in proc-macros.
#[doc(hidden)]
pub trait AssocStr {
    const STR: RStr<'static>;
}

macro_rules! impl_assoc_str {
    ( $($ty:ty),* ) => (
        $(
            impl AssocStr for $ty {
                const STR:RStr<'static>=RStr::from_str(stringify!( $ty ));
            }
        )*
    )
}

impl_assoc_str! { i8,i16,i32,i64,isize,u8,u16,u32,u64,usize }

//////////////////////////////////////////////////////////////////

// Used to test trait bounds in proc-macros.
#[doc(hidden)]
pub trait AssocInt {
    const NUM: usize;
}

macro_rules! impl_assoc_str {
    ( $($ty:ty=$val:expr),* $(,)* ) => (
        $(
            impl AssocInt for $ty {
                const NUM:usize=$val;
            }
        )*
    )
}

impl_assoc_str! {
    i8=0,i16=1,i32=2,i64=3,isize=4,
    u8=5,u16=6,u32=7,u64=8,usize=9,
}

//////////////////////////////////////

/// Creates an empty slice.
pub const fn empty_slice<'a, T>() -> &'a [T]
where
    T: 'a,
{
    GetEmptySlice::<'a, T>::EMPTY
}

struct GetEmptySlice<'a, T>(&'a T);

impl<'a, T> GetEmptySlice<'a, T>
where
    T: 'a,
{
    const EMPTY: &'a [T] = &[];
}

//////////////////////////////////////

macro_rules! min_max {
    ($l:expr, $r:expr) => {
        if $l < $r {
            ($l, $r)
        } else {
            ($r, $l)
        }
    };
}

/// The minimum of two `u64`s
pub const fn min_u8(l: u8, r: u8) -> u8 {
    min_max!(l, r).0
}

/// The minimum of two `u64`s
pub const fn min_u16(l: u16, r: u16) -> u16 {
    min_max!(l, r).0
}

/// The minimum of two `u64`s
pub const fn min_u64(l: u64, r: u64) -> u64 {
    min_max!(l, r).0
}

/// The minimum of two `usize`s
pub const fn min_usize(l: usize, r: usize) -> usize {
    min_max!(l, r).0
}

/// The maximum of two `u64`s
pub const fn max_u64(l: u64, r: u64) -> u64 {
    min_max!(l, r).1
}

/// The maximum of two `usize`s
pub const fn max_usize(l: usize, r: usize) -> usize {
    min_max!(l, r).1
}

/// The minimum and maximum of two `usize`s
pub const fn min_max_usize(l: usize, r: usize) -> (usize, usize) {
    min_max!(l, r)
}

//////////////////////////////////////

/// Gets the absolute value of a usize subtraction.
pub const fn abs_sub_usize(l: usize, r: usize) -> usize {
    let (min, max) = min_max_usize(l, r);
    max - min
}

//////////////////////////////////////

/// The base 2 logarithm of a usize.
pub const fn log2_usize(n: usize) -> u8 {
    const USIZE_BITS: u8 = (std::mem::size_of::<usize>() * 8) as u8;
    (USIZE_BITS - n.leading_zeros() as u8).saturating_sub(1)
}

//////////////////////////////////////

#[cfg(test)]
mod tests {
    use super::*;

    const USIZE_BITS: u8 = (std::mem::size_of::<usize>() * 8) as u8;

    #[test]
    fn abs_sub_test() {
        for p in 0..USIZE_BITS {
            let n = 1usize << p;
            assert_eq!(abs_sub_usize(0, n), n);
            assert_eq!(abs_sub_usize(n, 0), n);
        }
        assert_eq!(abs_sub_usize(4, 5), 1);
        assert_eq!(abs_sub_usize(5, 5), 0);
        assert_eq!(abs_sub_usize(5, 4), 1);
        assert_eq!(abs_sub_usize(5, 0), 5);
        assert_eq!(abs_sub_usize(0, 5), 5);
    }

    #[test]
    fn log2_usize_test() {
        assert_eq!(log2_usize(0), 0);
        assert_eq!(log2_usize(1), 0);
        for power in 1..USIZE_BITS {
            let n = 1usize << power;
            assert_eq!(log2_usize(n - 1), power - 1, "power:{} n:{}", power, n);
            assert_eq!(log2_usize(n), power, "power:{} n:{}", power, n);
            assert_eq!(log2_usize(n + 1), power, "power:{} n:{}", power, n);
        }
    }
}