[fpc-devel] Alternative parsers

[Alexander Klenin]

On Wed, Oct 20, 2010 at 01:45, Michael Van Canneyt
<michael at freepascal.org> wrote:

> If you need more convincing: the contnrs unit contains 2 hash classes.
> one based on ansistrings, one with pchars and shortstrings. The pchar
> version is easily 20% faster. It comes from the compiler code and was
> written specially by Peter Vreman.
>
> Try and improve that class with ansistrings. If you succeed, only then we
> can start making a case for using them in the compiler.

Ok, I went ahead and have taken look at the code.
I assume you speak about TFPHashList vs TFPCustomHashTable.
The classes are not really comparable, because they use quite
different internal data structures.
So instead I converted TFPHashList list to use ansistrings.

Benchmarking included 3*10^6 calls to Add and Find methods
with the arguments of various lengths.

Average string length 5 characters:
ShortString: 1.15 s
AnsiString: 1.56 s

Average string length 45 characters:
ShortString: 12.0 s
AnsiString: 3.2 s

I agree that the first case is more relevant for the compiler,
but still you can see that ShortStrings are clearly not always faster.

-- 
Alexander S. Klenin