epserde 0.12.5

ε-serde is an ε-copy (i.e., almost zero-copy) serialization/deserialization framework
Documentation 
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/*
 * SPDX-FileCopyrightText: 2023 Inria
 * SPDX-FileCopyrightText: 2023 Sebastiano Vigna
 *
 * SPDX-License-Identifier: Apache-2.0 OR LGPL-2.1-or-later
 */

//! Implementations for arrays.

use crate::prelude::*;
use core::hash::Hash;
use core::mem::MaybeUninit;
use deser::*;
use ser::*;

unsafe impl<T: CopyType, const N: usize> CopyType for [T; N] {
    type Copy = T::Copy;
}

impl<T: TypeHash, const N: usize> TypeHash for [T; N] {
    fn type_hash(hasher: &mut impl core::hash::Hasher) {
        "[]".hash(hasher);
        hasher.write_usize(N);
        T::type_hash(hasher);
    }
}

impl<T: AlignHash, const N: usize> AlignHash for [T; N] {
    fn align_hash(hasher: &mut impl core::hash::Hasher, offset_of: &mut usize) {
        if N == 0 {
            return;
        }
        T::align_hash(hasher, offset_of);
        *offset_of += (N - 1) * size_of::<T>();
    }
}

impl<T: AlignTo, const N: usize> AlignTo for [T; N] {
    fn align_to() -> usize {
        T::align_to()
    }
}

impl<T: CopyType + SerInner, const N: usize> SerInner for [T; N]
where
    [T; N]: SerHelper<<T as CopyType>::Copy>,
{
    type SerType = [T::SerType; N];
    const IS_ZERO_COPY: bool = T::IS_ZERO_COPY;
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        unsafe { SerHelper::_ser_inner(self, backend) }
    }
}

impl<T: ZeroCopy, const N: usize> SerHelper<Zero> for [T; N] {
    #[inline(always)]
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        ser_zero(backend, self)
    }
}

impl<T: DeepCopy, const N: usize> SerHelper<Deep> for [T; N] {
    unsafe fn _ser_inner(&self, backend: &mut impl WriteWithNames) -> ser::Result<()> {
        for item in self.iter() {
            backend.write("item", item)?;
        }
        Ok(())
    }
}

impl<T: CopyType + DeserInner, const N: usize> DeserInner for [T; N]
where
    [T; N]: DeserHelper<<T as CopyType>::Copy, FullType = [T; N]>,
{
    type DeserType<'a> = <[T; N] as DeserHelper<<T as CopyType>::Copy>>::DeserType<'a>;
    // SAFETY: In the Zero case, DeserType<'a> = &'a [T; N], which is covariant.
    // In the Deep case, DeserType<'a> = [T::DeserType<'a>; N]; arrays are
    // covariant in their element type, and T::DeserType is covariant
    // (enforced by T's own __check_covariance).
    crate::unsafe_assume_covariance!(T);

    #[inline(always)]
    unsafe fn _deser_full_inner(backend: &mut impl ReadWithPos) -> deser::Result<Self> {
        unsafe { <[T; N] as DeserHelper<<T as CopyType>::Copy>>::_deser_full_inner_impl(backend) }
    }

    #[inline(always)]
    unsafe fn _deser_eps_inner<'a>(
        backend: &mut SliceWithPos<'a>,
    ) -> deser::Result<<[T; N] as DeserHelper<<T as CopyType>::Copy>>::DeserType<'a>> {
        unsafe { <[T; N] as DeserHelper<<T as CopyType>::Copy>>::_deser_eps_inner_impl(backend) }
    }
}

impl<T: ZeroCopy + DeserInner, const N: usize> DeserHelper<Zero> for [T; N] {
    type FullType = Self;
    type DeserType<'a> = &'a [T; N];

    unsafe fn _deser_full_inner_impl(backend: &mut impl ReadWithPos) -> deser::Result<Self> {
        let mut res = MaybeUninit::<[T; N]>::uninit();
        backend.align::<T>()?;
        // SAFETY: read_exact guarantees that the array will be filled with data.
        unsafe {
            backend.read_exact(res.assume_init_mut().align_to_mut::<u8>().1)?;
            Ok(res.assume_init())
        }
    }

    unsafe fn _deser_eps_inner_impl<'a>(
        backend: &mut SliceWithPos<'a>,
    ) -> deser::Result<DeserType<'a, Self>> {
        backend.align::<T>()?;
        let bytes = core::mem::size_of::<[T; N]>();
        let (pre, data, after) = unsafe { backend.data[..bytes].align_to::<[T; N]>() };
        debug_assert!(pre.is_empty());
        debug_assert!(after.is_empty());
        let res = &data[0];
        backend.skip(bytes);
        Ok(res)
    }
}

impl<T: DeepCopy + DeserInner, const N: usize> DeserHelper<Deep> for [T; N] {
    type FullType = Self;
    type DeserType<'a> = [DeserType<'a, T>; N];

    unsafe fn _deser_full_inner_impl(backend: &mut impl ReadWithPos) -> deser::Result<Self> {
        let mut res = MaybeUninit::<[T; N]>::uninit();
        for item in &mut unsafe { res.assume_init_mut().iter_mut() } {
            unsafe { core::ptr::write(item, T::_deser_full_inner(backend)?) };
        }
        Ok(unsafe { res.assume_init() })
    }

    unsafe fn _deser_eps_inner_impl<'a>(
        backend: &mut SliceWithPos<'a>,
    ) -> deser::Result<DeserType<'a, Self>> {
        let mut res = MaybeUninit::<DeserType<'a, Self>>::uninit();
        for item in &mut unsafe { res.assume_init_mut().iter_mut() } {
            unsafe { core::ptr::write(item, T::_deser_eps_inner(backend)?) };
        }
        Ok(unsafe { res.assume_init() })
    }
}