(flex.info.gz) Is backing up a big deal?
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Is backing up a big deal?
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To: Adoram Rogel <adoram@hybridge.com>
Subject: Re: Flex 2.5.2 performance questions
In-reply-to: Your message of Thu, 19 Sep 96 10:16:04 EDT.
Date: Thu, 19 Sep 96 09:58:00 PDT
From: Vern Paxson <vern>
> a lot about the backing up problem.
> I believe that there lies my biggest problem, and I'll try to improve
> it.
Since you have variable trailing context, this is a bigger performance
problem. Fixing it is usually easier than fixing backing up, which in a
complicated scanner (yours seems to fit the bill) can be extremely
difficult to do correctly.
You also don't mention what flags you are using for your scanner.
-f makes a large speed difference, and -Cfe buys you nearly as much
speed but the resulting scanner is considerably smaller.
> I have an | operator in {and} and in {pats} so both of them are variable
> length.
-p should have reported this.
> Is changing one of them to fixed-length is enough ?
Yes.
> Is it possible to change the 32,000 states limit ?
Yes. I've appended instructions on how. Before you make this change,
though, you should think about whether there are ways to fundamentally
simplify your scanner - those are certainly preferable!
Vern
To increase the 32K limit (on a machine with 32 bit integers), you increase
the magnitude of the following in flexdef.h:
#define JAMSTATE -32766 /* marks a reference to the state that always jams */
#define MAXIMUM_MNS 31999
#define BAD_SUBSCRIPT -32767
#define MAX_SHORT 32700
Adding a 0 or two after each should do the trick.
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