flatbuffers/

array.rs

/*
 * Copyright 2021 Google Inc. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

use crate::follow::Follow;
use crate::vector::VectorIter;
use crate::EndianScalar;
use core::fmt::{Debug, Formatter, Result};
use core::marker::PhantomData;
use core::mem::size_of;

#[derive(Copy, Clone)]
pub struct Array<'a, T: 'a, const N: usize>(&'a [u8], PhantomData<T>);

impl<'a, T: 'a, const N: usize> Debug for Array<'a, T, N>
where
    T: 'a + Follow<'a>,
    <T as Follow<'a>>::Inner: Debug,
{
    fn fmt(&self, f: &mut Formatter) -> Result {
        f.debug_list().entries(self.iter()).finish()
    }
}

#[allow(clippy::len_without_is_empty)]
#[allow(clippy::from_over_into)] // TODO(caspern): Go from From to Into.
impl<'a, T: 'a, const N: usize> Array<'a, T, N> {
    /// # Safety
    ///
    /// buf must be a contiguous array of `T`
    ///
    /// # Panics
    ///
    /// Panics if `buf.len()` is not `size_of::<T>() * N`
    #[inline(always)]
    pub unsafe fn new(buf: &'a [u8]) -> Self {
        assert_eq!(size_of::<T>() * N, buf.len());

        Array(buf, PhantomData)
    }

    #[inline(always)]
    pub const fn len(&self) -> usize {
        N
    }
    pub fn as_ptr(&self) -> *const u8 {
        self.0.as_ptr()
    }
}

impl<'a, T: Follow<'a> + 'a, const N: usize> Array<'a, T, N> {
    #[inline(always)]
    pub fn get(&self, idx: usize) -> T::Inner {
        assert!(idx < N);
        let sz = size_of::<T>();
        // Safety:
        // self.0 was valid for length `N` on construction and have verified `idx < N`
        unsafe { T::follow(self.0, sz * idx) }
    }

    #[inline(always)]
    pub fn iter(&self) -> VectorIter<'a, T> {
        // Safety:
        // self.0 was valid for length N on construction
        unsafe { VectorIter::from_slice(self.0, self.len()) }
    }
}

impl<'a, T: Follow<'a> + Debug, const N: usize> From<Array<'a, T, N>> for [T::Inner; N] {
    fn from(array: Array<'a, T, N>) -> Self {
        array_init(|i| array.get(i))
    }
}

/// Implement Follow for all possible Arrays that have Follow-able elements.
impl<'a, T: Follow<'a> + 'a, const N: usize> Follow<'a> for Array<'a, T, N> {
    type Inner = Array<'a, T, N>;
    #[inline(always)]
    unsafe fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
        Array::new(&buf[loc..loc + N * size_of::<T>()])
    }
}

/// Place an array of EndianScalar into the provided mutable byte slice. Performs
/// endian conversion, if necessary.
/// # Safety
/// Caller must ensure `s.len() >= size_of::<[T; N]>()`
pub unsafe fn emplace_scalar_array<T: EndianScalar, const N: usize>(
    buf: &mut [u8],
    loc: usize,
    src: &[T; N],
) {
    let mut buf_ptr = buf[loc..].as_mut_ptr();
    for item in src.iter() {
        let item_le = item.to_little_endian();
        core::ptr::copy_nonoverlapping(
            &item_le as *const T::Scalar as *const u8,
            buf_ptr,
            size_of::<T::Scalar>(),
        );
        buf_ptr = buf_ptr.add(size_of::<T::Scalar>());
    }
}

impl<'a, T: Follow<'a> + 'a, const N: usize> IntoIterator for Array<'a, T, N> {
    type Item = T::Inner;
    type IntoIter = VectorIter<'a, T>;
    #[inline]
    fn into_iter(self) -> Self::IntoIter {
        self.iter()
    }
}

#[inline]
pub fn array_init<F, T, const N: usize>(mut initializer: F) -> [T; N]
where
    F: FnMut(usize) -> T,
{
    let mut array: core::mem::MaybeUninit<[T; N]> = core::mem::MaybeUninit::uninit();
    let mut ptr_i = array.as_mut_ptr() as *mut T;

    // Safety:
    // array is aligned by T, and has length N
    unsafe {
        for i in 0..N {
            let value_i = initializer(i);
            ptr_i.write(value_i);
            ptr_i = ptr_i.add(1);
        }
        array.assume_init()
    }
}

#[cfg(feature = "serialize")]
impl<'a, T: 'a, const N: usize> serde::ser::Serialize for Array<'a, T, N>
where
    T: 'a + Follow<'a>,
    <T as Follow<'a>>::Inner: serde::ser::Serialize,
{
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::ser::Serializer,
    {
        use serde::ser::SerializeSeq;
        let mut seq = serializer.serialize_seq(Some(self.len()))?;
        for element in self.iter() {
            seq.serialize_element(&element)?;
        }
        seq.end()
    }
}