Fix bugs when rounding to bignums

Also, since Emacs historically reported a range error when
rounding operations overflowed, do that consistently for all
bignum overflows.
* doc/lispref/errors.texi (Standard Errors):
* doc/lispref/numbers.texi (Integer Basics): Document range errors.
* src/alloc.c (range_error): Rename from integer_overflow.
All uses changed.
* src/floatfns.c (rounding_driver): When the result of a floating
point rounding operation does not fit into a fixnum, put it
into a bignum instead of always signaling an range error.
* test/src/floatfns-tests.el (divide-extreme-sign):
These tests now return the mathematically-correct answer
instead of signaling an error.
(bignum-round): Check that integers round to themselves.

1 files changed, 14 insertions, 2 deletions

diff --git a/src/floatfns.c b/src/floatfns.c
index c09fe9d6a5b..e7884864eef 100644
--- a/src/floatfns.c
+++ b/src/floatfns.c
@@ -410,7 +410,12 @@ rounding_driver (Lisp_Object arg, Lisp_Object divisor,
       if (! FIXNUM_OVERFLOW_P (ir))
         return make_fixnum (ir);
     }
-  xsignal2 (Qrange_error, build_string (name), arg);
+  mpz_t drz;
+  mpz_init (drz);
+  mpz_set_d (drz, dr);
+  Lisp_Object rounded = make_number (drz);
+  mpz_clear (drz);
+  return rounded;
 }
 
 static void
@@ -501,13 +506,20 @@ systems, but 2 on others.  */)
   return rounding_driver (arg, divisor, emacs_rint, rounddiv_q, "round");
 }
 
+/* Since rounding_driver truncates anyway, no need to call 'trunc'.  */
+static double
+identity (double x)
+{
+  return x;
+}
+
 DEFUN ("truncate", Ftruncate, Struncate, 1, 2, 0,
        doc: /* Truncate a floating point number to an int.
 Rounds ARG toward zero.
 With optional DIVISOR, truncate ARG/DIVISOR.  */)
   (Lisp_Object arg, Lisp_Object divisor)
 {
-  return rounding_driver (arg, divisor, trunc, mpz_tdiv_q, "truncate");
+  return rounding_driver (arg, divisor, identity, mpz_tdiv_q, "truncate");
 }