Re: GWT-client math vs. java-math

Thanks for posting about this Oskar. The radian/degree code can likely be changed (is that behavior specified as part of the Java spec?), though changing RPC serialization sounds like it would come with performance penalties - any comments there?

What is your preferred method of resolving the trig function issues - do you have a gwt-able java lib that you can suggest?

On Thursday, August 14, 2014 7:36:29 AM UTC-5, Oskar Stangenberg wrote:

Well, not every one of these things is easy to fix. Especially the trig-functions - GWT is probably using the js-internal ones - which are most likely pretty fast and good enough for client-only code. 

The server-impl of the trig-functions isn't even java-code - they are native functions. So their exact impl might even depend on the JRE used

Am Dienstag, 12. August 2014 19:45:08 UTC+2 schrieb Juan Pablo Gardella:

Thanks for sharing. It will very useful track each problem to GWT issue tracker.

2014-08-12 13:09 GMT-03:00 Oskar Stangenberg <crok...@gmail.com>:

Hi guys, we are developing a GWT-project with a lot of shared files. We discovered a few discrepancies in the gwt-math and server-math and wanted to share them for anybody else having those issues:

• First and foremost: all native double calculations are identical (+ - * / %)
• All trig-functions (sin,cos,tan,asin,acos,atan,atan2) seem to produces slightly different results. We recommend doing your own impl using lookup-maps
• sqrt,log and pow seem to be identical although we only tested sqrt thoroughly
• As far as we know all functions like max,min,abs etc are identical
• toDegrees and toRadian are actually different because GWT uses a constant for 180./PI and PI/180. which changes the order of operation compared to java
• For serialization of doubles we strongly suggest using Double.doubleToLongbits and Double.longBitsToDouble. You can additionally use Long.toString(long,32) and Long.parseString(string,32) to compress the String-representation
  

I hope we can help some people with this info. Especially the toDegrees/toRadians was very surprising to find. This issue was reported though and might be fixed in a future GWT-version (we tested 2.6.1).

In case you are interested how we solved the issues here is the open-source-part of our project so you can check it out

Regards

Oskar Stangenberg

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