private static Sha1 HashImpl(crypt.SHA1 alg, ReadOnlySpan <byte> span)
{
Debug.Assert(alg != null);
// Do NOT short-circuit here; rely on call-sites to do so
#if !NETSTANDARD2_0
Span <byte> hash = stackalloc byte[Sha1.ByteLength];
alg.TryComputeHash(span, hash, out _);
#else
var hash = alg.ComputeHash(span.ToArray());
#endif
var sha = new Sha1(hash);
return(sha);
}