fschutt
create_box_gauss() allocates needlessly
create_box_gauss() currently returns a Vec<i32> with length specified by the input parameter n. Vectors are always allocated on the heap, which is costly. Even the tiny vectors of 3 elements add 3% to the total runtime, or 6% in asymmetric case that calculates the box twice.
Sadly const generics are not yet implemented in rustc so we cannot abstract it over the length of a slice, but we can work around this e.g. by returning an iterator.
I'd wait for const generics. Const generics are coming pretty soon, I'm not sure how Iterators would solve the problem - you need at least one allocation (for the new, blurred image) and one allocation for the backbuffer.
Oh, the backbuffer is still needed. I'm talking about this allocation:
https://github.com/fschutt/fastblur/blob/3abecde49b3abdd73fe950e01eab9bf7b6e16dc9/src/blur.rs#L32
yeah, that could just be:
0..n.map(|i| if i < m { wl } else { wu }).collect();
I haven't worked on this crate in a long time, I just did this as a hobby at first.
.collect() would still allocate, but you can avoid collecting by returning the iterator directly. This is available since Rust 1.26: https://doc.rust-lang.org/edition-guide/rust-2018/trait-system/impl-trait-for-returning-complex-types-with-ease.html
The trait you want to return in this case is Iterator
Well, for Impl Iterator instead of allocations is actually slightly slower than allocating a Vec (well, my attempt is), so I guess arrays are the way to go.