The default file naming rule in GNAT is that the file name must be derived from the unit name. The exact default rule is as follows:
switch of the compiler activates a "krunching"
circuit that limits file names to nn characters (where nn is a decimal
integer). For example, using OpenVMS,
where the maximum file name length is
39, the value of nn is usually set to 39, but if you want to generate
a set of files that would be usable if ported to a system with some
different maximum file length, then a different value can be specified.
The default value of 39 for OpenVMS need not be specified.
gnatkr utility can be used to determine the krunched name for
a given file, when krunched to a specified maximum length.