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