Mojo Deflate vs. C

A Mojo implementation of DEFLATE, built with Claude's assistance, narrowly outperformed libdeflate, the C library described as the performance benchmark for the compression format. The author, who also had Claude build a mutation tester for Mojo called despell, reported that Claude used Mojo's comptime feature for minor optimizations to edge ahead, and noted the same tricks could be implemented in C but would be more cumbersome. The result, published in the mojo-deflate repository, follows Richard Feldman's post on how close pure functional programming can get to C performance.

Mojo deflate vs C I read Richard Feldman’s post How close can pure FP get to C? https://rtfeldman.com/fp-vs-c , and this quote caught my attention: However, the article https://kim-em.github.io/blog/2026-7-24-why-lean-is-faster-than-rust/ also notes that while they managed to surpass Rust’s miniz oxide, they were no match for the end boss of DEFLATE performance: libdeflate, written in C. I’ve been playing around with Mojo https://mojolang.org/ , and I wondered how close to C performance we could get, so I sent Claude on it. Along the way I had Claude build a mutation tester for Mojo that I named despell https://github.com/boxed/despell . All in all, the Mojo version https://github.com/boxed/mojo-deflate managed to beat libdeflate, if only by a narrow margin. Claude found some minor tricks it could employ very easily with Mojo’s comptime feature to edge ahead. As Claude also said, this could all be implemented in the C version too, it’s just a bit more cumbersome.