Avoid some excess precision in time arithmetic

* doc/misc/emacs-mime.texi (time-date):
Adjust example to match new behavior.
* etc/NEWS: Mention this.
* lisp/calendar/time-date.el (decoded-time-add)
(decoded-time--alter-second):
Don’t lose underestimate precision of seconds component.
* src/bignum.c (mpz): Grow by 1.
* src/timefns.c (trillion_factor): New function.
(timeform_sub_ps_p): Remove.
(time_arith): Avoid unnecessarily-large hz, by reducing the hz
to a value no worse than the worse hz of the two arguments.
The result is always exact unless an error is signaled.
* test/src/timefns-tests.el (timefns-tests--decode-time):
New function.
(format-time-string-with-zone): Test (decode-time LOOK ZONE t)
resolution as well as its numeric value.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/bignum.h b/src/bignum.h
index a9c7a0a09a8..9a32ffb0374 100644
--- a/src/bignum.h
+++ b/src/bignum.h
@@ -41,7 +41,7 @@ struct Lisp_Bignum
   mpz_t value;
 } GCALIGNED_STRUCT;
 
-extern mpz_t mpz[4];
+extern mpz_t mpz[5];
 
 extern void init_bignum (void);
 extern Lisp_Object make_integer_mpz (void);