XF86VidModeGetGammaRampSize(3) on Linux

The text a84ef02812cd, as Debian 13 (Trixie), Debian 12 (Bookworm), Debian 11 (Bullseye), Debian 10 (Buster), Debian 9 (Stretch) shipped it.

Extension library for the XFree86-VidMode X extension