In general, new metering functions are implemented using the bucket primitive. No change to tcc is needed for this.
The file tcng/tcc/meters.tc.in contains the definitions of the meters which are part of the tcng language.
meters.tc.in uses a special pseudo preprocessor directive called
#map. This directive is converted by tcng/tcc/tcc_var2fix.pl
to a set of macros for elements with a tcng-style parameter list.
Please consult the source code of /tcc_var2fix.pl for a detailed
description of these macros.