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

// This file is part of ICU4X. For terms of use, please see the file
// called LICENSE at the top level of the ICU4X source tree
// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).

pub(crate) trait MaybeSplitAt<T> {
    /// Like slice::split_at but returns an Option instead of panicking
    /// if the index is out of range.
    fn maybe_split_at(&self, mid: usize) -> Option<(&Self, &Self)>;
    /// Like slice::split_at but debug-panics and returns an empty second slice
    /// if the index is out of range.
    fn debug_split_at(&self, mid: usize) -> (&Self, &Self);
}

impl<T> MaybeSplitAt<T> for [T] {
    #[inline]
    fn maybe_split_at(&self, mid: usize) -> Option<(&Self, &Self)> {
        if mid > self.len() {
            None
        } else {
            // Note: We're trusting the compiler to inline this and remove the assertion
            // hiding on the top of slice::split_at: `assert(mid <= self.len())`
            Some(self.split_at(mid))
        }
    }
    #[inline]
    fn debug_split_at(&self, mid: usize) -> (&Self, &Self) {
        if mid > self.len() {
            debug_assert!(false, "debug_split_at: index expected to be in range");
            (self, &[])
        } else {
            // Note: We're trusting the compiler to inline this and remove the assertion
            // hiding on the top of slice::split_at: `assert(mid <= self.len())`
            self.split_at(mid)
        }
    }
}

pub(crate) trait DebugUnwrapOr<T> {
    /// Unwraps the option or panics in debug mode, returning the `gigo_value`
    fn debug_unwrap_or(self, gigo_value: T) -> T;
}

impl<T> DebugUnwrapOr<T> for Option<T> {
    #[inline]
    fn debug_unwrap_or(self, gigo_value: T) -> T {
        match self {
            Some(x) => x,
            None => {
                debug_assert!(false, "debug_unwrap_or called on a None value");
                gigo_value
            }
        }
    }
}

macro_rules! debug_unwrap {
    ($expr:expr, return $retval:expr, $($arg:tt)+) => {
        match $expr {
            Some(x) => x,
            None => {
                debug_assert!(false, $($arg)*);
                return $retval;
            }
        }
    };
    ($expr:expr, return $retval:expr) => {
        debug_unwrap!($expr, return $retval, "invalid trie")
    };
    ($expr:expr, break, $($arg:tt)+) => {
        match $expr {
            Some(x) => x,
            None => {
                debug_assert!(false, $($arg)*);
                break;
            }
        }
    };
    ($expr:expr, break) => {
        debug_unwrap!($expr, break, "invalid trie")
    };
    ($expr:expr, $($arg:tt)+) => {
        debug_unwrap!($expr, return (), $($arg)*)
    };
    ($expr:expr) => {
        debug_unwrap!($expr, return ())
    };
}

pub(crate) use debug_unwrap;

/// The maximum number of base-10 digits required for rendering a usize.
/// Note: 24/10 is an approximation of 8*log10(2)
pub(crate) const MAX_USIZE_LEN_AS_DIGITS: usize = core::mem::size_of::<usize>() * 24 / 10 + 1;

/// Formats a usize as a string of length N, padded with spaces,
/// with the given prefix.
///
/// If the string is too short, the function may panic. To prevent
/// this, N should be MAX_USIZE_LEN_AS_DIGITS larger than M.
pub(crate) const fn const_fmt_int<const M: usize, const N: usize>(
    prefix: [u8; M],
    value: usize,
) -> [u8; N] {
    let mut output = [b' '; N];
    let mut i = 0;
    while i < M {
        output[i] = prefix[i];
        i += 1;
    }
    let mut int_only = [b' '; MAX_USIZE_LEN_AS_DIGITS];
    let mut value = value;
    let mut i = MAX_USIZE_LEN_AS_DIGITS - 1;
    loop {
        let x = (value % 10) as u8;
        int_only[i] = x + b'0';
        value /= 10;
        if value == 0 {
            break;
        }
        i -= 1;
    }
    let mut j = M;
    while i < MAX_USIZE_LEN_AS_DIGITS {
        output[j] = int_only[i];
        j += 1;
        i += 1;
    }
    output
}

#[test]
fn test_const_fmt_int() {
    assert_eq!(*b"123", const_fmt_int::<0, 3>(*b"", 123));
    assert_eq!(*b"123   ", const_fmt_int::<0, 6>(*b"", 123));
    assert_eq!(*b"abc123", const_fmt_int::<3, 6>(*b"abc", 123));
}