flatbuffers/
array.rs

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1/*
2 * Copyright 2021 Google Inc. All rights reserved.
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *     http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17use crate::follow::Follow;
18use crate::vector::VectorIter;
19use crate::EndianScalar;
20use core::fmt::{Debug, Formatter, Result};
21use core::marker::PhantomData;
22use core::mem::size_of;
23
24#[derive(Copy, Clone)]
25pub struct Array<'a, T: 'a, const N: usize>(&'a [u8], PhantomData<T>);
26
27impl<'a, T: 'a, const N: usize> Debug for Array<'a, T, N>
28where
29    T: 'a + Follow<'a>,
30    <T as Follow<'a>>::Inner: Debug,
31{
32    fn fmt(&self, f: &mut Formatter) -> Result {
33        f.debug_list().entries(self.iter()).finish()
34    }
35}
36
37#[allow(clippy::len_without_is_empty)]
38#[allow(clippy::from_over_into)] // TODO(caspern): Go from From to Into.
39impl<'a, T: 'a, const N: usize> Array<'a, T, N> {
40    /// # Safety
41    ///
42    /// buf must be a contiguous array of `T`
43    ///
44    /// # Panics
45    ///
46    /// Panics if `buf.len()` is not `size_of::<T>() * N`
47    #[inline(always)]
48    pub unsafe fn new(buf: &'a [u8]) -> Self {
49        assert_eq!(size_of::<T>() * N, buf.len());
50
51        Array(buf, PhantomData)
52    }
53
54    #[inline(always)]
55    pub const fn len(&self) -> usize {
56        N
57    }
58    pub fn as_ptr(&self) -> *const u8 {
59        self.0.as_ptr()
60    }
61}
62
63impl<'a, T: Follow<'a> + 'a, const N: usize> Array<'a, T, N> {
64    #[inline(always)]
65    pub fn get(&self, idx: usize) -> T::Inner {
66        assert!(idx < N);
67        let sz = size_of::<T>();
68        // Safety:
69        // self.0 was valid for length `N` on construction and have verified `idx < N`
70        unsafe { T::follow(self.0, sz * idx) }
71    }
72
73    #[inline(always)]
74    pub fn iter(&self) -> VectorIter<'a, T> {
75        // Safety:
76        // self.0 was valid for length N on construction
77        unsafe { VectorIter::from_slice(self.0, self.len()) }
78    }
79}
80
81impl<'a, T: Follow<'a> + Debug, const N: usize> From<Array<'a, T, N>> for [T::Inner; N] {
82    fn from(array: Array<'a, T, N>) -> Self {
83        array_init(|i| array.get(i))
84    }
85}
86
87/// Implement Follow for all possible Arrays that have Follow-able elements.
88impl<'a, T: Follow<'a> + 'a, const N: usize> Follow<'a> for Array<'a, T, N> {
89    type Inner = Array<'a, T, N>;
90    #[inline(always)]
91    unsafe fn follow(buf: &'a [u8], loc: usize) -> Self::Inner {
92        Array::new(&buf[loc..loc + N * size_of::<T>()])
93    }
94}
95
96/// Place an array of EndianScalar into the provided mutable byte slice. Performs
97/// endian conversion, if necessary.
98/// # Safety
99/// Caller must ensure `s.len() >= size_of::<[T; N]>()`
100pub unsafe fn emplace_scalar_array<T: EndianScalar, const N: usize>(
101    buf: &mut [u8],
102    loc: usize,
103    src: &[T; N],
104) {
105    let mut buf_ptr = buf[loc..].as_mut_ptr();
106    for item in src.iter() {
107        let item_le = item.to_little_endian();
108        core::ptr::copy_nonoverlapping(
109            &item_le as *const T::Scalar as *const u8,
110            buf_ptr,
111            size_of::<T::Scalar>(),
112        );
113        buf_ptr = buf_ptr.add(size_of::<T::Scalar>());
114    }
115}
116
117impl<'a, T: Follow<'a> + 'a, const N: usize> IntoIterator for Array<'a, T, N> {
118    type Item = T::Inner;
119    type IntoIter = VectorIter<'a, T>;
120    #[inline]
121    fn into_iter(self) -> Self::IntoIter {
122        self.iter()
123    }
124}
125
126#[inline]
127pub fn array_init<F, T, const N: usize>(mut initializer: F) -> [T; N]
128where
129    F: FnMut(usize) -> T,
130{
131    let mut array: core::mem::MaybeUninit<[T; N]> = core::mem::MaybeUninit::uninit();
132    let mut ptr_i = array.as_mut_ptr() as *mut T;
133
134    // Safety:
135    // array is aligned by T, and has length N
136    unsafe {
137        for i in 0..N {
138            let value_i = initializer(i);
139            ptr_i.write(value_i);
140            ptr_i = ptr_i.add(1);
141        }
142        array.assume_init()
143    }
144}
145
146#[cfg(feature = "serialize")]
147impl<'a, T: 'a, const N: usize> serde::ser::Serialize for Array<'a, T, N>
148where
149    T: 'a + Follow<'a>,
150    <T as Follow<'a>>::Inner: serde::ser::Serialize,
151{
152    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
153    where
154        S: serde::ser::Serializer,
155    {
156        use serde::ser::SerializeSeq;
157        let mut seq = serializer.serialize_seq(Some(self.len()))?;
158        for element in self.iter() {
159            seq.serialize_element(&element)?;
160        }
161        seq.end()
162    }
163}
flatbuffers/array.rs

flatbuffers/
array.rs
