invalid generated public key

Hello,
thanks for your work. I wanted to play with your implementation on both a 64 bits PC and a 16bits PIC24F µC. I played with k163 curve.

On PC, it works like a charm (although it generates a public key filled with 0x00 when I build in release and works in debug) but on the PIC24F, it takes around 30s (!) to execute ecdh_generate_keys() and the final result is a public key filled with 0x00. May I have incorrectly used it so that it generates such a public key? Is the implementation supposed to work on 16bits CPUs?

Start at ecdh_generate_keys() and reproduce the k163 result on the 64-bit PC in both debug and release builds, then on the 16-bit PIC24F. Compare the generated public-key output and execution time to determine whether the zero key is caused by portability or build behavior; done means the supported behavior on 16-bit CPUs and the cause of the invalid output are established.

Written by the indexing model from the issue text.