Can you try the rpm instead?
In any case, as said in my previous post, the proposed code is unusable.
-G
Good news!
This new version works fine with all the value types and behaves as I expected. In this case I use the bias parameter to adjust the curve (like I commented in my very first post) and it has even easier maths inside. In particular there is not need to tweak the parameter to match the desired behavior in all the cases of values and times.
Here are the binaries:
sourceforge.net/projects/synfig/ … -binaries/
The old binaries have been deleted so you have to download and install the genete_new_interpolation from 2012/01/07
Cheers!
-G
Here two sample images:
I love, love, love it! And, if you’re not too embarrased by it, I love you to Genete for making this!
One of my biggest gripes with Synfig since I started using it is solved! 
Now I’m off to do some thorough testing of this.
Oh, this is just incredible - I can see this coming in very handy!
Many thanks Genete! 
superb 
Uploaded binaries on sf have complete support for clamped interpolations. It was missing the clamped option on Edit Waypoint dialog and Keyframe Settings dialog. Now it is implemented.
Enjoy!
-G