> Many GNU/Linux distros (at least Debian and RHEL) install neither `dc` nor `bc` by default, afaik.

Yeah, I recently wrote a script that used bc and immediately discovered that it didn't work on at least Arch Linux (and I think others, although I only seem to have added it to the Arch ansible config...); conveniently, I only needed the most trivial of calculations, so I just shifted to awk, which has better default availability.

Gentoo doesn't include it in the common 'stage3' tarball, either. Which is annoying because it's actually required to compile the linux kernel.

I stand corrected, only bc is included in POSIX.