Always allow at least double-precision bignums

Without this fix, Emacs can get into a tight loop reporting
a range error when calculating timestamps.
* doc/lispref/numbers.texi (Integer Basics):
* src/alloc.c (syms_of_alloc): Document this.
* src/bignum.c (make_bignum_bits): Always allow bignums
of at least twice the width of (u)intmax_t.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/alloc.c b/src/alloc.c
index 5c5b56d02e9..64aaa8acdfa 100644
--- a/src/alloc.c
+++ b/src/alloc.c
@@ -7369,9 +7369,9 @@ The time is in seconds as a floating point value.  */);
               doc: /* Accumulated number of garbage collections done.  */);
 
   DEFVAR_INT ("integer-width", integer_width,
-              doc: /* Maximum number of bits in bignums.
-Integers outside the fixnum range are limited to absolute values less
-than 2**N, where N is this variable's value.  N should be nonnegative.  */);
+              doc: /* Maximum number N of bits in safely-calculated integers.
+Integers with absolute values less than 2**N do not signal a range error.
+N should be nonnegative.  */);
 
   defsubr (&Scons);
   defsubr (&Slist);