recode 0.4.1

Reusable encoding/decoding constructs for Rust
Documentation 
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use crate::bytes::{Buf, BufMut};
use crate::util::EncoderExt;
use crate::{Decoder, Encoder};

pub use ux::{i24, i40, i48, i56, u24, u40, u48, u56};

macro_rules! impl_ux {
    ($t:ty; size: $s:literal; rep: $r:ty ) => {
        impl<B: Buf> Decoder<B> for $t {
            type Error = crate::Error;

            fn decode(buf: &mut B) -> Result<Self, Self::Error> {
                const REPR_LEN: usize = std::mem::size_of::<$r>();

                if buf.remaining() < $s {
                    return Err(crate::Error::BytesNeeded {
                        needed: $s - buf.remaining(),
                        full_len: $s,
                        available: buf.remaining(),
                    });
                }

                let mut be_repr = [0u8; REPR_LEN];
                buf.copy_to_slice(&mut be_repr[(REPR_LEN - $s)..REPR_LEN]);

                Ok(<$t>::new(<$r>::from_be_bytes(be_repr)))
            }
        }

        impl<B: BufMut> Encoder<B> for $t {
            type Error = std::convert::Infallible;

            fn encode(item: &$t, buf: &mut B) -> Result<(), Self::Error> {
                const REPR_LEN: usize = std::mem::size_of::<$r>();

                let bytes = &<$r>::from(*item).to_be_bytes()[(REPR_LEN - $s)..];

                buf.put_slice(bytes);

                Ok(())
            }

            #[inline]
            fn size_of(_: &$t, _: &B) -> usize {
                $s
            }
        }

        impl<B: Buf> Decoder<B, usize> for $t {
            type Error = crate::Error;

            fn decode(buf: &mut B) -> Result<usize, Self::Error> {
                let value = <Self as crate::Decoder<B>>::decode(buf)?;

                usize::try_from(<$r>::from(value))
                    .map_err(|_| super::number::TryFromIntError(()))
                    .map_err(Into::into)
            }
        }

        impl<B: BufMut> Encoder<B, usize> for $t {
            type Error = crate::Error;

            fn encode(item: &usize, buf: &mut B) -> Result<(), Self::Error> {
                let value = <$r>::try_from(*item)
                    .map_err(|_| super::number::TryFromIntError(()))?;

                <$t>::new(value).encode_to(buf).map_err(Into::into)
            }

            #[inline]
            fn size_of(_: &usize, _: &B) -> usize {
                $s
            }
        }
    };
}

impl_ux!(i24; size: 3; rep: i32);
impl_ux!(u24; size: 3; rep: u32);

impl_ux!(i40; size: 5; rep: i64);
impl_ux!(u40; size: 5; rep: u64);

impl_ux!(i48; size: 6; rep: i64);
impl_ux!(u48; size: 6; rep: u64);

impl_ux!(i56; size: 7; rep: i64);
impl_ux!(u56; size: 7; rep: u64);

#[cfg(test)]
mod tests {
    use bytes::BytesMut;
    use fake::Fake;

    use super::*;
    use crate::util::EncoderExt;

    macro_rules! test_ux {
        ($t:ty; size: $s:literal; rep: $r:ty ) => {
            paste::paste! {
                #[test]
                fn [<test_ $t>]() {
                    const REPR_LEN: usize = std::mem::size_of::<$r>();

                    let rmax: $r = <$t>::MAX.into();
                    let repr: $r = (0..rmax).fake();

                    if stringify!($t).starts_with("u") {
                        assert_eq!(rmax.trailing_ones(), $s * 8);
                    } else {
                        assert_eq!(rmax.trailing_ones(), $s * 8 - 1);
                    }

                    assert_eq!(repr & !rmax, 0);

                    let value = <$t>::new(repr);
                    let mut bytes = BytesMut::new();

                    assert_eq!($s, value.size(&bytes));

                    value.encode_to(&mut bytes).unwrap();

                    assert_eq!($s, bytes.len());
                    assert_eq!(&repr.to_be_bytes()[(REPR_LEN - $s)..], &bytes[..]);
                }
            }
        };
    }

    test_ux!(i24; size: 3; rep: i32);
    test_ux!(u24; size: 3; rep: u32);

    test_ux!(i40; size: 5; rep: i64);
    test_ux!(u40; size: 5; rep: u64);

    test_ux!(i48; size: 6; rep: i64);
    test_ux!(u48; size: 6; rep: u64);

    test_ux!(i56; size: 7; rep: i64);
    test_ux!(u56; size: 7; rep: u64);
}