This lets us extract large integers without involving math/big. While at it, drop some use of reflect where a type switch will do. Change-Id: Iebe2fb2267610bf95cf9747ba1d49b5ac9e62cda Reviewed-on: https://go-review.googlesource.com/c/crypto/+/451515 Run-TryBot: Filippo Valsorda <filippo@golang.org> Reviewed-by: Damien Neil <dneil@google.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Roland Shoemaker <roland@golang.org> TryBot-Result: Gopher Robot <gobot@golang.org> Auto-Submit: Filippo Valsorda <filippo@golang.org>