Don't rely on bignums in ntlm.el

Since ntlm.el is distributed as a separate package in GNU ELPA and
should be able to run on older Emacs versions without bignums,
we cannot make use of them here.  See discussion at
https://lists.gnu.org/archive/html/emacs-devel/2020-10/msg01665.html.
Instead, we add a small poor man's bignum implementation.

* lisp/net/ntlm.el (ntlm--bignat-of-int, ntlm--bignat-add)
(ntlm--bignat-shift-left, ntlm--bignat-mul-byte, ntlm--bignat-mul)
(ntlm--bignat-of-string, ntlm--bignat-of-digits)
(ntlm--bignat-to-int64): New.
(ntlm--time-to-timestamp): Use the ntlm--bignat- functions instead
of Lisp integers.
* test/lisp/net/ntlm-tests.el: New file.

1 files changed, 52 insertions, 0 deletions

diff --git a/test/lisp/net/ntlm-tests.el b/test/lisp/net/ntlm-tests.el
new file mode 100644
index 00000000000..e515ebe2635
--- /dev/null
+++ b/test/lisp/net/ntlm-tests.el
@@ -0,0 +1,52 @@
+;;; ntlm-tests.el --- tests for ntlm.el            -*- lexical-binding: t -*-
+
+;; Copyright (C) 2020 Free Software Foundation, Inc.
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
+
+(require 'ert)
+(require 'ntlm)
+
+;; This is the Lisp bignum implementation of `ntlm--time-to-timestamp',
+;; for reference.
+(defun ntlm-tests--time-to-timestamp (time)
+  "Convert TIME to an NTLMv2 timestamp.
+Return a unibyte string representing the number of tenths of a
+microsecond since January 1, 1601 as a 64-bit little-endian
+signed integer.  TIME must be on the form (HIGH LOW USEC PSEC)."
+  (let* ((s (+ (ash (nth 0 time) 16) (nth 1 time)))
+         (us (nth 2 time))
+         (ps (nth 3 time))
+         (tenths-of-us-since-jan-1-1601
+          (+ (* s 10000000) (* us 10) (/ ps 100000)
+             ;; tenths of microseconds between 1601-01-01 and 1970-01-01
+             116444736000000000)))
+    (apply #'unibyte-string
+           (mapcar (lambda (i)
+                     (logand (ash tenths-of-us-since-jan-1-1601 (* i -8))
+                             #xff))
+                   (number-sequence 0 7)))))
+
+(ert-deftest ntlm-time-to-timestamp ()
+  ;; Verify poor man's bignums in implementation that can run on Emacs < 27.1.
+  (let ((time '(24471 63910 412962 0)))
+    (should (equal (ntlm--time-to-timestamp time)
+                   (ntlm-tests--time-to-timestamp time))))
+  (let ((time '(397431 65535 999999 999999)))
+    (should (equal (ntlm--time-to-timestamp time)
+                   (ntlm-tests--time-to-timestamp time)))))
+
+(provide 'ntlm-tests)