1//! Utilities to help with buffering.
2
3#![allow(unsafe_code)]
4
5use core::mem::MaybeUninit;
6use core::slice;
7
8/// Split an uninitialized byte slice into initialized and uninitialized parts.
9///
10/// # Safety
11///
12/// `init_len` must not be greater than `buf.len()`, and at least `init_len`
13/// bytes must be initialized.
14#[inline]
15pub(super) unsafe fn split_init(
16 buf: &mut [MaybeUninit<u8>],
17 init_len: usize,
18) -> (&mut [u8], &mut [MaybeUninit<u8>]) {
19 debug_assert!(init_len <= buf.len());
20 let buf_ptr: *mut MaybeUninit = buf.as_mut_ptr();
21 let uninit_len: usize = buf.len() - init_len;
22 let init: &mut [u8] = slice::from_raw_parts_mut(data:buf_ptr.cast::<u8>(), init_len);
23 let uninit: &mut [MaybeUninit] = slice::from_raw_parts_mut(data:buf_ptr.add(count:init_len), uninit_len);
24 (init, uninit)
25}
26
27#[cfg(test)]
28mod tests {
29 use super::*;
30
31 #[test]
32 fn test_split_init() {
33 let mut input_array = [
34 MaybeUninit::new(0_u8),
35 MaybeUninit::new(1_u8),
36 MaybeUninit::new(2_u8),
37 MaybeUninit::new(3_u8),
38 ];
39 let input_array_clone = input_array.clone();
40 let input_array_ptr = input_array.as_ptr();
41 let output_array = [0_u8, 1_u8, 2_u8, 3_u8];
42
43 unsafe {
44 let (init, uninit) = split_init(&mut input_array, 0);
45 assert_eq!(init, &[]);
46 assert_eq!(uninit.len(), input_array_clone.len());
47 assert_eq!(uninit.as_ptr(), input_array_ptr);
48
49 let (init, uninit) = split_init(&mut input_array, input_array_clone.len());
50 assert_eq!(init, &output_array[..]);
51 assert_eq!(init.as_ptr(), input_array_ptr.cast());
52 assert_eq!(uninit.len(), 0);
53 assert_eq!(
54 uninit.as_ptr(),
55 input_array_ptr.add(input_array_clone.len())
56 );
57
58 let (init, uninit) = split_init(&mut input_array, 2);
59 assert_eq!(init, &output_array[..2]);
60 assert_eq!(init.as_ptr(), input_array_ptr.cast());
61 assert_eq!(uninit.len(), 2);
62 assert_eq!(uninit.as_ptr(), input_array_ptr.add(2));
63 }
64 }
65
66 #[test]
67 fn test_split_init_empty() {
68 unsafe {
69 let (init, uninit) = split_init(&mut [], 0);
70 assert!(init.is_empty());
71 assert!(uninit.is_empty());
72 }
73 }
74}
75