How close can pure FP get to C?
Roc’s DEFLATE compressor is now close to C’s libdeflate on the author’s benchmark: its median was 8.9% slower on a Ryzen 9 3900X and 2.6% slower on an M1. The comparison is encouraging, but it is a focused result, not evidence that Roc generally matches C: the work targets non-streaming APIs, uses one corpus, and includes deliberate low-level optimization.
The article describes measured changes such as prefetching and bounds checks that help the compiler optimize loops. In the 11-comment Lobsters discussion, readers praised opportunistic mutation, asked whether the optimized code is idiomatic, and emphasized that languages differ in ergonomics and guarantees rather than their theoretical performance ceiling.