[computer-go] Re: C in Java

[Weimin Xiao]

Very interesting. Can you provide sample code of writing C style program 
using Java?

Weimin

----- Original Message ----- 
From: "Chrilly" <c.donninger at wavenet.at>
To: "computer-go" <computer-go at computer-go.org>
Sent: Monday, July 24, 2006 1:00 AM
Subject: Re: [computer-go] Monte Carlo combined with minimax search


>I have ported a C chess programm which was initially written for a Hitachi 
>microcontroller to Java. The Java version was on a PC only 15% slower. One 
>can write C-programs in Java with the rules below. The 15% difference are 
>due to the better optimization of a C-Compiler. The Java to Virtual-Machine 
>compiler produces very poor code. Obviously the Just-In-Time compiler in 
>the runtime does only some loophole optimizations which can not compete 
>with the optimizations of a C-Compiler. When switching off the JIT-Compiler 
>the Java code runs 15 times slower.
>
> The rules to produce very fast Java codes are:
>
> a) Avoid new, any creation of new objects.
> b) Function/method codes are in Java expensive, because the correct method 
> is determined dynamically. I C its a simply "call" instruction. The 
> standard Java calling convention is by orders more expensive than in C. To 
> circumvent this problem one has to declare the class as final. In this 
> case the compiler can generate also a "call" instruction like in C. In my 
> program there was only one big final class which contained all the 
> functions/methods of the original code. I removed effectivly the 
> object-system and wrote a flat-collection of functions like in plain C.
> c) The Java Virtual Engine can only process 32-Bit numbers. All other data 
> are second class citizens which are converted to 32-Bit. Using e.g. a Byte 
> array makes things worse, because there is an additional Convert to 32-Bit 
> instruction involved. In case of the chess programm, everything was packed 
> as much as possible, because the Hitachi had only 4KByte of RAM. I had to 
> blow up things to ints or used the trick described in d).
> d) Do NOT convert C-structs to Java classes. The C-original used  a lot of 
> 4 Byte structures with 4  1-Byte Elements. E.g a move is encode as struct 
> { Uint8 from, Uint8 to, Uint8 flags, Sint8 val; }
> I converted this to a 32-Bit integer and exctracted the fields with 
> bit-fiddling. This is much faster and compact than converting the struct 
> to a class. But it produces ugly and error-prone code.
> One could also use 4 int arrays. But the conversion was closer to the 
> original. Additionally is the 32-Bit fiddling method more cache-friendly.
>
> I did this as a programming excercise, but I see no point of writing bad C 
> Code in Java.
>
> Chrilly
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