/usr.bin/yacc/NOTES

1Berkeley Yacc reflects its origins.  The reason so many routines
2use exactly six register variables is that Berkeley Yacc was
3developed on a VAX using PCC.  PCC placed at most six variables
4in registers.  I went to considerable effort to find which six
5variables most belonged in registers.  Changes in machines and
6compilers make that effort worthless, perhaps even harmful.
7
8The code contains many instances where address calculations are
9performed in particular ways to optimize the code for the VAX.