Module zeroed_alloc

This module is for allocating large arrays or vectors with initial zero values.

Currently we use the [Zeroable] trait from the bytemuck crate to label types that are safe for zero initialization. If one day Rust provides a standard way to optimize for zeroed allocation of vectors of composite types, we can switch to the standard mechanism.

Note: The standard library uses the IsZero trait to specialize the intialization of Vec<T> if the initial element values are zero. Primitive type, such as i8, usize, f32, as well as types with known representations such as Option<NonZeroUsize> implement the IsZero trait. However, it has several limitations.

1. Composite types, such as SpaceDescriptor(usize), don’t implement the IsZero trait, even if they have the #[repr(transparent)] annotation.
2. The IsZero trait is private to the std module, and we cannot use it.

Therefore, vec![0usize; 33554432] takes only 4 microseconds, while vec![SpaceDescriptor(0); 33554432] will take 22 milliseconds to execute on some machine. If such an allocation happens during start-up, the delay will be noticeable to light-weight scripting languages, such as Ruby.

The new_zeroed_vec function in this module can allocate zeroed vectors as fast as vec![0; LEN];

Functions

• new_zeroed_vec 🔒
  Allocate a Vec<T> of all-zero values. T must implement [bytemuck::Zeroable].