How Bitcoin Core calculate extended private masterkey from hdseed I am testing a Bitcoin application, and to test the signing of transactions I use regtest with Bitcoin Core. But I have some problems, the first I have already published in a question that I still have no convenient answer.

But the problem generated by this new question is:

If a Bitcoin Core wallet can be saved and loaded with just the hdseed, then the extended private masterkey is calculated from it. Then, how Bitcoin Core calculate that?

Thanks in advance
Conversion from a HD seed to a master private key is specified by BIP 32.

It is done by computing a HMAC-SHA512 where the key is the text Bitcoin seed and the data is the HD seed itself. The first 32 bytes (256 bits) is the master private key. The last 32 byte is the chaincode for the master key.