castflip 0.1.15

Library for encoding/decoding numeric variables, arrays and structures in little-endian and big-endian
Documentation 
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

use core::mem;

use crate::Cast;
use crate::experimental::Reslice;


///
/// Defines methods to convert a reference to a slice into a
/// transmuted reference to a variable of the specified type without
/// copying data.
///
/// The antonym of [`Deslice`] is [`Enslice`].
///
/// [`Enslice`]: ./trait.Enslice.html
///
/// # Example
///
/// In the example below, method `deslice` converts the original
/// reference to bytes `bytes1` into a transmuted reference to type
/// `ElfIdHdr` without copying data.
///
/// ```
/// # fn main() { test(); }
/// # fn test() -> Option<()> {
/// use castflip::experimental::Deslice;
/// use castflip::Cast;
///
/// #[repr(C)]
/// #[derive(Cast)]
/// struct ElfIdHdr {
///     magic:    [u8; 4],  //00-03: Magic Number 0x7F "ELF"
///     class:    u8,       //04   : File Class
///     encoding: u8,       //05   : Data Encoding
///     version:  u8,       //06   : Version (should be 1)
///     os_abi:   u8,       //07   : OS and ABI
///     abi_ver:  u8,       //08   : ABI Version
///     pad:      [u8; 7],  //09-0F: Padding (should be 0)
/// }
///
/// // Input data: ELF Identification (16 bytes)
/// let bytes1: [u8; 16] = [0x7F, 0x45, 0x4C, 0x46, 0x02, 0x01, 0x01, 0x00,
///                         0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00];
///
/// unsafe {
///     // Convert the original reference to `bytes1` into `hdr`.
///     // Both &`bytes1` and `hdr` point to the same entity.
///     let hdr: &ElfIdHdr = bytes1.deslice()?;
///
///     // Check the results (hdr)
///     assert_eq!(&hdr.magic, b"\x7FELF"); // Magic Number: 7F 45 4C 46
///     assert_eq!(hdr.class, 2);           // File Class: 64-bit
///     assert_eq!(hdr.encoding, 1);        // Data Encoding: Little-Endian
///     assert_eq!(hdr.version, 1);         // Version 1
///     assert_eq!(hdr.os_abi, 0);          // (unspecified)
///     assert_eq!(hdr.abi_ver, 0);         // (unspecified)
///     assert_eq!(hdr.pad, [0_u8; 7]);     // Padding
/// }
/// # Some(())
/// # }
/// ```
///
/// Note: [ELF] is a common standard file format for executable files.
/// ELF Identification is the first 16 bytes of the ELF header.
///
/// [ELF]: https://en.wikipedia.org/wiki/Executable_and_Linkable_Format
///
/// # Description
///
/// All methods in trait `Deslice` convert a reference to a slice into
/// a transmuted reference to a variable of the specified type without
/// copying data.
///
/// The size of the original slice and the size of the transmuted
/// variable must be the same.  And the address of the original slice
/// must satisfy the requirement of the alignment of the transmuted
/// variable.  If these requirements are satisfied, resulting
/// reference is returned in `Some`().  Otherwise, None is returned.
///
/// # Safety
///
/// We do not understand clearly what kind of problems could occur
/// with this trait.
///
/// Because the Rust compiler would not recognize what is happening,
/// it may reorder instructions unexpectedly.  When a transmuted
/// reference is created by this trait, it would be better not to use
/// the original reference until the transmuted reference is dropped,
/// expecially when the original reference is mutable.
///
/// When creating a transmuted reference with this trait, take care with
/// the alignment issues.
///
pub trait Deslice {
    /// Converts a reference to the slice `self` of a type
    /// into a transmuted reference to a variable of type `U`.
    unsafe fn deslice<U>(&self) -> Option<&U>
    where
        U: Cast;

    /// Converts a mutable reference to the slice `self` of a type
    /// into a mutable transmuted reference to a variable of type `U`.
    unsafe fn deslice_mut<U>(&mut self) -> Option<&mut U>
    where
        U: Cast;
}


impl<T> Deslice for [T]
where
    T: Cast,
{
    unsafe fn deslice<U>(&self) -> Option<&U>
    where
        U: Cast,
    {
        if mem::size_of::<T>() * self.len() == mem::size_of::<U>() {
            let slice1 = unsafe { self.reslice::<U>()? };
            Some(&slice1[0])
        } else {
            None
        }
    }

    unsafe fn deslice_mut<U>(&mut self) -> Option<&mut U>
    where
        U: Cast,
    {
        if mem::size_of::<T>() * self.len() == mem::size_of::<U>() {
            let slice1 = unsafe { self.reslice_mut::<U>()? };
            Some(&mut slice1[0])
        } else {
            None
        }
    }
}