Well TIL that printf won't lock stdout. Calling stdout.lock() by itself makes little difference for me. Using BufWriter as you have I get ~80 MiB/s (slightly a

Well TIL that printf won't lock stdout. Calling stdout.lock() by itself makes little difference for me. Using BufWriter as you have I get ~80 MiB/s (slightly ahead of PyPy). My implementation also has/had a String allocation in the loop, kicking that out got me to 120 MiB/s. I tend to write it as though the numbers/strings could be changed by a product manager at any time. Final edit/errata: I get up to 140 MiB/s by appending .to_string() in the integer case instead of format!(), which makes some sense. I didn't bother saving my original C implementation, but in retrospect I think I didn't use string concatenation, as I have with other languages. Redoing it with string-concatenation, C is slightly slower than Rust, 110 MiBs. Also makes sense as concatenation in C is slow.