1use crate::mem::MaybeUninit;
2
3/// Trait used to describe the maximum number of digits in decimal base of the implemented integer.
4#[unstable(feature = "int_format_into", issue = "138215")]
5pub trait NumBufferTrait {
6 /// Maximum number of digits in decimal base of the implemented integer.
7 const BUF_SIZE: usize;
8}
9
10macro_rules! impl_NumBufferTrait {
11 ($($signed:ident, $unsigned:ident,)*) => {
12 $(
13 #[unstable(feature = "int_format_into", issue = "138215")]
14 impl NumBufferTrait for $signed {
15 // `+ 2` and not `+ 1` to include the `-` character.
16 const BUF_SIZE: usize = $signed::MAX.ilog(10) as usize + 2;
17 }
18 #[unstable(feature = "int_format_into", issue = "138215")]
19 impl NumBufferTrait for $unsigned {
20 const BUF_SIZE: usize = $unsigned::MAX.ilog(10) as usize + 1;
21 }
22 )*
23 }
24}
25
26impl_NumBufferTrait! {
27 i8, u8,
28 i16, u16,
29 i32, u32,
30 i64, u64,
31 isize, usize,
32 i128, u128,
33}
34
35/// A buffer wrapper of which the internal size is based on the maximum
36/// number of digits the associated integer can have.
37#[unstable(feature = "int_format_into", issue = "138215")]
38#[derive(Debug)]
39pub struct NumBuffer<T: NumBufferTrait> {
40 // FIXME: Once const generics feature is working, use `T::BUF_SIZE` instead of 40.
41 pub(crate) buf: [MaybeUninit<u8>; 40],
42 // FIXME: Remove this field once we can actually use `T`.
43 phantom: core::marker::PhantomData<T>,
44}
45
46#[unstable(feature = "int_format_into", issue = "138215")]
47impl<T: NumBufferTrait> NumBuffer<T> {
48 /// Initializes internal buffer.
49 #[unstable(feature = "int_format_into", issue = "138215")]
50 pub const fn new() -> Self {
51 // FIXME: Once const generics feature is working, use `T::BUF_SIZE` instead of 40.
52 NumBuffer { buf: [MaybeUninit::<u8>::uninit(); 40], phantom: core::marker::PhantomData }
53 }
54
55 /// Returns the length of the internal buffer.
56 #[unstable(feature = "int_format_into", issue = "138215")]
57 pub const fn capacity(&self) -> usize {
58 self.buf.len()
59 }
60}
61