https://benchmarksgame-team.pages.debian.net/benchmarksgame/performance/revcomp.html
Demonstrates a good performance (at least top 5), while has half the memory usage. Currently it's not much different from other solutions unless some efficient multithreading is implemented.
Build with gcc -pipe -Wall -O3 -fomit-frame-pointer -march=native revcomp.c -o revcomp
Single threaded, yet slightly faster than https://benchmarksgame-team.pages.debian.net/benchmarksgame/program/revcomp-python3-6.html
(6.8 s run time of my version vs 9.7 s for python3-6 on dual core VM FreeBSD 12.0, Win7 Skylake host)