pub unsafe extern "C" fn mbedtls_ecdsa_sign(
grp: *mut mbedtls_ecp_group,
r: *mut mbedtls_mpi,
s: *mut mbedtls_mpi,
d: *const mbedtls_mpi,
buf: *const c_uchar,
blen: usize,
f_rng: Option<unsafe extern "C" fn(arg1: *mut c_void, arg2: *mut c_uchar, arg3: usize) -> c_int>,
p_rng: *mut c_void,
) -> c_int