[antlr-interest] Inefficiency in lexer

[Terence Parr]

On May 27, 2005, at 12:19 PM, ttest wrote:

> Hi again,
>
> I'm not sure if Java is really that smart. I would think that LA(1) is
> compared to every character one at a time which would be inefficient.
>
> What would the lookup table look like?
>
> I guess the key in the table would be the char returned by LA(1)  
> and what
> would the values be in that table? The memory location where execution
> continues?
>
> Then the lookup table would be 2^16*6=393216=390K bytes big which  
> would be
> pretty much.

Java VMs claim to do a binary search for sparse data and a look up  
table for contiguous data.  In this case, binary search is the best  
we can do with a switch.  Sometimes an IF is better.

Ter
--
CS Professor & Grad Director, University of San Francisco
Creator, ANTLR Parser Generator, http://www.antlr.org
Cofounder, http://www.jguru.com