1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
|
use core::ptr;
use crate::alloc::Allocator;
use crate::raw_vec::RawVec;
use super::{IsZero, Vec};
// Specialization trait used for Vec::from_elem
pub(super) trait SpecFromElem: Sized {
fn from_elem<A: Allocator>(elem: Self, n: usize, alloc: A) -> Vec<Self, A>;
}
impl<T: Clone> SpecFromElem for T {
default fn from_elem<A: Allocator>(elem: Self, n: usize, alloc: A) -> Vec<Self, A> {
let mut v = Vec::with_capacity_in(n, alloc);
v.extend_with(n, elem);
v
}
}
impl<T: Clone + IsZero> SpecFromElem for T {
#[inline]
default fn from_elem<A: Allocator>(elem: T, n: usize, alloc: A) -> Vec<T, A> {
if elem.is_zero() {
return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n };
}
let mut v = Vec::with_capacity_in(n, alloc);
v.extend_with(n, elem);
v
}
}
impl SpecFromElem for i8 {
#[inline]
fn from_elem<A: Allocator>(elem: i8, n: usize, alloc: A) -> Vec<i8, A> {
if elem == 0 {
return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n };
}
let mut v = Vec::with_capacity_in(n, alloc);
unsafe {
ptr::write_bytes(v.as_mut_ptr(), elem as u8, n);
v.set_len(n);
}
v
}
}
impl SpecFromElem for u8 {
#[inline]
fn from_elem<A: Allocator>(elem: u8, n: usize, alloc: A) -> Vec<u8, A> {
if elem == 0 {
return Vec { buf: RawVec::with_capacity_zeroed_in(n, alloc), len: n };
}
let mut v = Vec::with_capacity_in(n, alloc);
unsafe {
ptr::write_bytes(v.as_mut_ptr(), elem, n);
v.set_len(n);
}
v
}
}
// A better way would be to implement this for all ZSTs which are `Copy` and have trivial `Clone`
// but the latter cannot be detected currently
impl SpecFromElem for () {
#[inline]
fn from_elem<A: Allocator>(_elem: (), n: usize, alloc: A) -> Vec<(), A> {
let mut v = Vec::with_capacity_in(n, alloc);
// SAFETY: the capacity has just been set to `n`
// and `()` is a ZST with trivial `Clone` implementation
unsafe {
v.set_len(n);
}
v
}
}
|