1234949SbaptBerkeley Yacc reflects its origins.  The reason so many routines
2234949Sbaptuse exactly six register variables is that Berkeley Yacc was
3234949Sbaptdeveloped on a VAX using PCC.  PCC placed at most six variables
4234949Sbaptin registers.  I went to considerable effort to find which six
5234949Sbaptvariables most belonged in registers.  Changes in machines and
6234949Sbaptcompilers make that effort worthless, perhaps even harmful.
7234949Sbapt
8234949SbaptThe code contains many instances where address calculations are
9234949Sbaptperformed in particular ways to optimize the code for the VAX.
10