From Erlang Community

0) run configure

1) add your bifs to erts/emulator/beam/bif.tab

bif re:grep/2
bif re:compile/1

2) create a C file

erts/emulator/beam/erl_bif_re.c

3) add your C file to erts/emulator/<arch>/Makefile

RUN_OBJS = $(OBJDIR)/erl_bif_re.o \

4) implement your bifs by stealing bits from existing erl_bif_*.c files

BIF_RETTYPE re_grep_2(BIF_ALIST_2){
  Eterm result;
  result = magic_function(); 
  BIF_RET(result);
}

5) run make; make install

steps 0-3 need only be done once.

note that if you add

bif re:grep/2

to bif.tab there should be a

erl_bif_re.c

that implements

BIF_RETTYPE re_grep_2(BIF_ALIST_2);