This is a vendored version of paritytech/libsecp256k1 with only what secp256kfun needs from it.
Copyright
Copyright Parity Technologies (UK) Ltd.
Originally Written by Wei Tang.
Licensed under the Apache License Version 2.0
Code was originally copied from https://github.com/paritytech/libsecp256k1
at commit: d453081f81579b03f8ce8c56494779185f0cc29c