Add module functions to convert from and to big integers.

* src/module-env-27.h: Add new module functions to convert big
integers.

* src/emacs-module.h.in (emacs_mpz): Define if GMP is available.

* src/emacs-module.c (module_extract_big_integer)
(module_make_big_integer): New functions.
(initialize_environment): Use them.

* test/data/emacs-module/mod-test.c (Fmod_test_double): New test
function.
(emacs_module_init): Define it.

* test/src/emacs-module-tests.el (mod-test-double): New unit test.

* doc/lispref/internals.texi (Module Values): Document new functions.

2 files changed, 26 insertions, 0 deletions

diff --git a/test/data/emacs-module/mod-test.c b/test/data/emacs-module/mod-test.c
index dbdbfecfe6a..85a7f28e50d 100644
--- a/test/data/emacs-module/mod-test.c
+++ b/test/data/emacs-module/mod-test.c
@@ -27,8 +27,11 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include <string.h>
 #include <time.h>
 
+#define EMACS_MODULE_GMP
 #include <emacs-module.h>
 
+#include <gmp.h>
+
 #include "timespec.h"
 
 int plugin_is_GPL_compatible;
@@ -378,6 +381,21 @@ Fmod_test_add_nanosecond (emacs_env *env, ptrdiff_t nargs, emacs_value *args,
   return env->make_time (env, time);
 }
 
+static emacs_value
+Fmod_test_double (emacs_env *env, ptrdiff_t nargs, emacs_value *args,
+                  void *data)
+{
+  assert (nargs == 1);
+  emacs_value arg = args[0];
+  struct emacs_mpz value;
+  mpz_init (value.value);
+  env->extract_big_integer (env, arg, &value);
+  mpz_mul_ui (value.value, value.value, 2);
+  emacs_value result = env->make_big_integer (env, &value);
+  mpz_clear (value.value);
+  return result;
+}
+
 /* Lisp utilities for easier readability (simple wrappers).  */
 
 /* Provide FEATURE to Emacs.  */
@@ -447,6 +465,7 @@ emacs_module_init (struct emacs_runtime *ert)
          NULL, NULL);
   DEFUN ("mod-test-sleep-until", Fmod_test_sleep_until, 2, 2, NULL, NULL);
   DEFUN ("mod-test-add-nanosecond", Fmod_test_add_nanosecond, 1, 1, NULL, NULL);
+  DEFUN ("mod-test-double", Fmod_test_double, 1, 1, NULL, NULL);
 
 #undef DEFUN
 
diff --git a/test/src/emacs-module-tests.el b/test/src/emacs-module-tests.el
index eea4c611655..78f238140da 100644
--- a/test/src/emacs-module-tests.el
+++ b/test/src/emacs-module-tests.el
@@ -338,4 +338,11 @@ Interactively, you can try hitting \\[keyboard-quit] to quit."
     (ert-info ((format "input: %s" input))
       (should-error (mod-test-add-nanosecond input)))))
 
+(ert-deftest mod-test-double ()
+  (dolist (input (list 0 1 2 -1 42 12345678901234567890
+                       most-positive-fixnum (1+ most-positive-fixnum)
+                       most-negative-fixnum (1- most-negative-fixnum)))
+    (ert-info ((format "input: %d" input))
+      (should (= (mod-test-double input) (* 2 input))))))
+
 ;;; emacs-module-tests.el ends here