To sanity check myself, I reran this without the buffered reader and still don't see the slow execution time:

> echo '60016000526001601ff3' | xxd -r -p > | zig build run -Doptimize=ReleaseFast

> execution time: 28.889µs

So I think my machine config for whatever reason isn't representative of whatever OP is using.

Linux-ck 6.8 CONFIG_NO_HZ=y CONFIG_HZ_1000=y

Intel 13900k

zig 0.11

bash 5.2.26

xxd 2024-02-10

Would be good if someone that can repro it compares the two invocation variants with buffered reader implemented & lists their config.