试图通过 unsafe 绕过越界检查看越界检查有多少额外开销

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<T>(*mut T); impl<T> From<*const T> for Array<T> { fn from(ptr: *const T) -> Self { Self(ptr as *mut _) } } impl<T> std::ops::Index<usize> for Array<T> { type Output = T; fn index(&self, index: usize) -> &Self::Output { unsafe { let ptr = self.0.offset(index as isize); &*ptr } } } impl<T> std::ops::IndexMut<usize> for Array<T> { 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::<usize>() % 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::<usize>() % SIZE; arr[index] += 1; } } let elapsed = start.elapsed(); println!("Array indexing without boundary check runtime: {}ms", elapsed.as_millis()); }