共计 1064 个字符,预计需要花费 3 分钟才能阅读完成。
结果在我的 M2 Mac mini 上,
- 有边界检查: 1152 ms
- 无边界检查: 1084 ms
基本是 6% 左右的时间开销 (不确定我这个封装是否有额外开销).
附源代码:
struct Array(*mut T);
impl From<*const T> for Array {fn from(ptr: *const T) -> Self {Self(ptr as *mut _)
}
}
impl std::ops::Index for Array {
type Output = T;
fn index(&self, index: usize) -> &Self::Output {
unsafe {let ptr = self.0.offset(index as isize);
&*ptr
}
}
}
impl std::ops::IndexMut for Array {fn index_mut(&mut self, index: usize) -> &mut Self::Output {
unsafe {let ptr = self.0.offset(index as isize);
&mut *ptr
}
}
}
fn main() {
const SIZE: usize = 1024 * 1024;
const LOOP: usize = 2_000_000;
let mut arr = vec![0u32; SIZE];
let start = std::time::Instant::now();
// array indexing with boundary check
{
for _ in 0..LOOP {let index = rand::random::() % SIZE;
arr[index] += 1;
}
}
let elapsed = start.elapsed();
println!("Array indexing with boundary check runtime: {}ms", elapsed.as_millis());
// to avoid cache, use a different raw array.
let mut arr = Array::from(vec![0u32; SIZE].as_ptr());
let start = std::time::Instant::now();
// array indexing wthout boundary check
{
for _ in 0..LOOP {let index = rand::random::() % SIZE;
arr[index] += 1;
}
}
let elapsed = start.elapsed();
println!("Array indexing without boundary check runtime: {}ms", elapsed.as_millis());
}
正文完