I have been constructing division algorithms and want some feedback

[Aaron Kutch]

I have spent much time optimizing a set of division algorithms for Rust’s `compiler-builtins` (a pure Rust version of LLVM’s `compiler-rt`). I am emailing to gmp-discuss because I think my 128 bit `_trifecta` and `asymmetric` algorithms could act as good base cases for division functions in GMP, and because I don’t know any group of people other than those in GMP who could better review my algorithms. I ran a simple benchmark of dividing a random 128 bit integer with a 64 bit random integer and found that GMP took 21 microseconds to calculate it using `Integer::div_rem_mut` (using the Rust `rug` crate which binds to GMP), while my `specialized_div_rem::u128_div_rem_asymmetric` function took only 1.2 microseconds. I understand that my function deals with integers on the stack and has fewer function call overheads, but division is such an expensive operation that I would not expect much difference if the internal algorithms performed similarly. The Git repo for my algorithms is https://github.com/AaronKutch/specialized-div-rem, the crates.io link is https://crates.io/crates/specialized-div-rem, and the in-progress PR for `compiler-builtins` is https://github.com/rust-lang/compiler-builtins/pull/332.