Function bip85::to_xprv

pub fn to_xprv<C: Signing>(
    secp: &Secp256k1<C>, 
    root: &ExtendedPrivKey, 
    index: u32
) -> Result<ExtendedPrivKey, Error>

Derive bip32 extended private key from root xprv

See specs for more info.

index can be any number lower than 0x80000000