Re: Hash specifics

In article <2980@lupine.NCD.COM> rfg@ncd.com (Ron Guilmette) writes:
      Henry's point is well taken, however there are *some* places where I think
      that it is probably worth the effort to try to find a *perfect* hash
      function. Keyword tables in compilers and opcode tables in assemblers
      come to mind.


The time when I always find myself looking for a perfect hash function, is
when I am parsing long keyword options (ie: -ansi etc...) or some other case
when I have a small set of possibilities but want to avoid using:


if (!strcmp("hello", arg))
{}
else if (!strcmp("there", arg))
{}
else if (!strcmp("world", arg))
{}
                else
error;


Maybe I'm just being silly, but the above code, and the tiny hand crafted
lexers I usually end up both make me gag.


Because these situations often come up several times within one program I'd
much rather put in a quick perfect hash, then have to put in the code to deal
with collisions.


I have one program where I ended up having 15 or so different instances of
this situation. I ended up giving them start conditions and just calling
the (already terribly complicated) flex lexer, but that seems like overkill
for everyday use.


/Evan
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