This function is intended for use in tag summarizers where the tag has
already been stripped. It expects a CBOR byte string representing n where
the actual value is -1 - n (tag 3 content per RFC 8949).
Enforces canonical encoding: no leading zero bytes (except single 0x00
for -1).
Decode a BigInt from an untagged CBOR byte string for a negative bignum.
Matches Rust's
bigint_from_negative_untagged_cbor().This function is intended for use in tag summarizers where the tag has already been stripped. It expects a CBOR byte string representing
nwhere the actual value is-1 - n(tag 3 content per RFC 8949).Enforces canonical encoding: no leading zero bytes (except single
0x00for -1).