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| 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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