Hi recently when I use the secp256k1 library to generate the test vector, I find that EOS add some more API into the "official secp256k1" lib of bitcoin. For Exp, for signature generating, EOS lib API provides one more function "secp256k1_ecdsa_sign_compact"--there is one similar API is ""secp256k1_ecdsa_sign". They both produce the 64byte signature. Initially, I thought this would be a similar tricky like a "compact" signature that ETH to compress recid--which only impact the 1st byte of the key.
But later found, if using the same private key and digest, "secp256k1_ecdsa_sign_compact" and "secp256k1_ecdsa_sign" will produce the completely different signature, not only 1 byte different. Can any one help to explain why was that?