Does openFHE support comparison?

Library Questions
1

does openFHE support some function that can do the comparison of 2 encrypted numbers?

2

yes, see openfhe-development/eval-sign.cpp at main · openfheorg/openfhe-development · GitHub It is based on TFHE/FHEW. The algorithm is described/proposed in Large-Precision Homomorphic Sign Evaluation using FHEW/TFHE Bootstrapping

1 Like
3

Thank you very much for replying! I run exact same code in eval-sign.cpp, but got some thing like: “openfhe-development/src/binfhe/lib/fhew.cpp:914 ERROR: EvalSign is only for large precision. For small precision, please use bootstrapping directly”. What does that means?

4

I just ran the example using the default settings, i.e., when \log Q=17, and it worked without any problems. Did you try to run it for a smaller \log Q? This would cause the exception to be thrown. In the current implementation Q needs to be larger than q.

As a side note, the case of Q=q (1 bootstrapping) requires a trickier API now, and we can make it simpler to use (i.e., we can add support for it directly to EvalSign). Is this the case you tried?

5

hi, i didn’t change anything in the eval-sign.cpp, and i got:
logQ: 17
Q: 131072
q: 4096
factor: 32
p: 512
but i still got the error “EvalSign is only for large precision. For small precision, please use bootstrapping directly”. I run the code on MacBook with M2 chip, would that affect the result?

6

  1. As a sanity check can you give us more details? E.g what macbook make, compiler, etc.?

  2. Have you followed all the instructions listed out in our discord Installing OpenFHE on MacOS

7

Thank you very much! I reinstall the whole thing and it worked!

8

Amazing! Thank you and please mark this as solved since it osunds like we addressed all your questions :slight_smile: