integer_encoding/
fixed.rs

1use std::convert::TryInto;
2use std::mem::size_of;
3
4/// `FixedInt` provides encoding/decoding to and from fixed int representations. Note that current
5/// Rust versions already provide this functionality via the `to_le_bytes()` and `to_be_bytes()`
6/// methods.
7///
8/// The emitted bytestring contains the bytes of the integer in machine endianness.
9pub trait FixedInt: Sized + Copy {
10    type Bytes: AsRef<[u8]>;
11    const ENCODED_SIZE: usize = size_of::<Self>();
12
13    /// Encode a value into the given slice using little-endian. Returns `None` if `dst`
14    /// doesn't provide enough space to encode this integer.
15    ///
16    /// Use `switch_endianness()` if machine endianness doesn't match the desired target encoding.
17    fn encode_fixed(self, dst: &mut [u8]) -> Option<()>;
18    /// Returns the representation of [`FixedInt`] as [`Bytes`], the little-endian representation
19    /// of self in the stack.
20    fn encode_fixed_light(self) -> Self::Bytes;
21
22    /// Decode a value from the given slice assuming little-endian. Use `switch_endianness()` on
23    /// the returned value if the source was not encoded in little-endian.
24    fn decode_fixed(src: &[u8]) -> Option<Self>;
25
26    /// Helper: Encode the value and return a Vec.
27    fn encode_fixed_vec(self) -> Vec<u8> {
28        self.encode_fixed_light().as_ref().to_vec()
29    }
30
31    /// integer-encoding-rs always emits and receives little-endian integers (converting implicitly
32    /// on big-endian machines). If you receive a big-endian integer, and would like it to be
33    /// treated correctly, use this helper method to convert between endiannesses.
34    fn switch_endianness(self) -> Self;
35}
36
37macro_rules! impl_fixedint {
38    ($t:ty) => {
39        impl FixedInt for $t {
40            type Bytes = [u8; size_of::<$t>()];
41
42            fn encode_fixed(self, dst: &mut [u8]) -> Option<()> {
43                if dst.len() == size_of::<Self>() {
44                    dst.clone_from_slice(&self.to_le_bytes());
45                    Some(())
46                } else {
47                    None
48                }
49            }
50
51            fn encode_fixed_light(self) -> Self::Bytes {
52                self.to_le_bytes()
53            }
54
55            fn decode_fixed(src: &[u8]) -> Option<Self> {
56                if src.len() == size_of::<Self>() {
57                    Some(Self::from_le_bytes(src.try_into().unwrap()))
58                } else {
59                    None
60                }
61            }
62
63            fn switch_endianness(self) -> Self {
64                Self::from_le_bytes(self.to_be_bytes())
65            }
66        }
67    };
68}
69
70impl_fixedint!(usize);
71impl_fixedint!(u64);
72impl_fixedint!(u32);
73impl_fixedint!(u16);
74impl_fixedint!(u8);
75impl_fixedint!(isize);
76impl_fixedint!(i64);
77impl_fixedint!(i32);
78impl_fixedint!(i16);
79impl_fixedint!(i8);
integer_encoding/fixed.rs

integer_encoding/
fixed.rs
