Hey, OP here.
Code not written by me, but by a friend (iscgar) with no HN account.
On my late 2019 MacBook Pro, using clang 12.
clang -O3 -march=native fizz4.c
./a.out | pv > /dev/null
Starts at around 4GiB/s and drops down to 3.8 after a while, probably due to battery/heating.
