Improve time stamp handling, and be more consistent about it.

This implements a suggestion made in:
http://lists.gnu.org/archive/html/emacs-devel/2014-10/msg00587.html
Among other things, this means timer.el no longer needs to
autoload the time-date module.
* doc/lispref/os.texi (Time of Day, Time Conversion, Time Parsing)
(Processor Run Time, Time Calculations):
Document the new behavior, plus be clearer about the old behavior.
(Idle Timers): Take advantage of new functionality.
* etc/NEWS: Document the changes.
* lisp/allout-widgets.el (allout-elapsed-time-seconds): Doc fix.
* lisp/arc-mode.el (archive-ar-summarize):
* lisp/calendar/time-date.el (seconds-to-time, days-to-time, time-since):
* lisp/emacs-lisp/timer.el (timer-relative-time, timer-event-handler)
(run-at-time, with-timeout-suspend, with-timeout-unsuspend):
* lisp/net/tramp.el (tramp-time-less-p, tramp-time-subtract):
* lisp/proced.el (proced-time-lessp):
* lisp/timezone.el (timezone-time-from-absolute):
* lisp/type-break.el (type-break-schedule, type-break-time-sum):
Simplify by using new functionality.
* lisp/calendar/cal-dst.el (calendar-next-time-zone-transition):
Do not return time values in obsolete and undocumented (HI . LO)
format; use (HI LO) instead.
* lisp/calendar/time-date.el (with-decoded-time-value):
Treat 'nil' as current time.  This is mostly for XEmacs.
(encode-time-value, with-decoded-time-value): Obsolete.
(time-add, time-subtract, time-less-p): Use no-op autoloads, for
XEmacs.  Define only if XEmacs, as they're now C builtins in Emacs.
* lisp/ldefs-boot.el: Update to match new time-date.el
* lisp/proced.el: Do not require time-date.
* src/editfns.c (invalid_time): New function.
Use it instead of 'error ("Invalid time specification")'.
(time_add, time_subtract, time_arith, Ftime_add, Ftime_less_p)
(decode_float_time, lisp_to_timespec, lisp_time_struct):
New functions.
(make_time_tail, make_time): Remove.  All uses changed to use
new functions or plain list4i.
(disassemble_lisp_time): Return effective length if successful.
Check that LOW is an integer, if it's combined with other components.
(decode_time_components): Decode into struct lisp_time, not
struct timespec, so that we can support a wide set of times
regardless of whether time_t is signed.  Decode plain numbers
as seconds since the Epoch, and nil as the current time.
(lisp_time_argument, lisp_seconds_argument, Ffloat_time):
Reimplement in terms of new functions.
(Fencode_time): Just use list2i.
(syms_of_editfns): Add time-add, time-subtract, time-less-p.
* src/keyboard.c (decode_timer): Don't allow the new formats (floating
point or nil) in timers.
* src/systime.h (LO_TIME_BITS): New constant.  Use it everywhere in
place of the magic number '16'.
(struct lisp_time): New type.
(decode_time_components): Use it.
(lisp_to_timespec): New decl.

19 files changed, 548 insertions, 327 deletions

diff --git a/doc/lispref/ChangeLog b/doc/lispref/ChangeLog
index b7423af07ba..0a8a0a88cce 100644
--- a/doc/lispref/ChangeLog
+++ b/doc/lispref/ChangeLog
@@ -1,3 +1,11 @@
+2014-11-17  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Improve time stamp handling, and be more consistent about it.
+        * os.texi (Time of Day, Time Conversion, Time Parsing)
+        (Processor Run Time, Time Calculations):
+        Document the new behavior, plus be clearer about the old behavior.
+        (Idle Timers): Take advantage of new functionality.
+
 2014-11-16  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * text.texi (Special Properties): Mention `inhibit-read-only'.
diff --git a/doc/lispref/os.texi b/doc/lispref/os.texi
index 167ecb372b5..b7094479db2 100644
--- a/doc/lispref/os.texi
+++ b/doc/lispref/os.texi
@@ -1213,37 +1213,34 @@ return value is @code{nil}.
 zone.
 
 @cindex epoch
-  Most of these functions represent time as a list of either four
-integers, @code{(@var{sec-high} @var{sec-low} @var{microsec}
-@var{picosec})}, or of three
-integers, @code{(@var{sec-high} @var{sec-low} @var{microsec})}, or of
-two integers, @code{(@var{sec-high} @var{sec-low})}.  The integers
-@var{sec-high} and @var{sec-low} give the high and low bits of an
-integer number of seconds.  This integer,
+  Most of these functions represent time as a list of four integers
+@code{(@var{sec-high} @var{sec-low} @var{microsec} @var{picosec})}.
+This represents the number of seconds from the @dfn{epoch} (January
+1, 1970 at 00:00 UTC), using the formula:
 @ifnottex
-@var{high} * 2**16 + @var{low},
+@var{high} * 2**16 + @var{low} + @var{micro} * 10**@minus{}6 +
+@var{pico} * 10**@minus{}12.
 @end ifnottex
 @tex
-$high*2^{16}+low$,
+$high*2^{16} + low + micro*10^{-6} + pico*10^{-12}$.
 @end tex
-is the number of seconds from the @dfn{epoch} (January 1, 1970 at 00:00
-UTC) to the specified time.  The third list element @var{microsec}, if
-present, gives the number of microseconds from the start of that
-second to the specified time.
-Similarly, the fourth list element @var{picosec}, if present, gives
-the number of picoseconds from the start of that microsecond to the
-specified time.
-
-  The return value of @code{current-time} represents time using four
-integers, as do the timestamps in the return value of
-@code{file-attributes} (@pxref{Definition of
-file-attributes}).  In function arguments, e.g., the @var{time-value}
-argument to @code{current-time-string}, two-, three-, and four-integer
-lists are accepted.  You can convert times from the list
-representation into standard human-readable strings using
-@code{current-time-string}, or to other forms using the
-@code{decode-time} and @code{format-time-string} functions documented
-in the following sections.
+The return value of @code{current-time} represents time using this
+form, as do the timestamps in the return values of other functions
+such as @code{file-attributes} (@pxref{Definition of
+file-attributes}).  In some cases, functions may return two- or
+three-element lists, with omitted @var{microsec} and @var{picosec}
+components defaulting to zero.
+
+@cindex time value
+  Function arguments, e.g., the @var{time-value} argument to
+@code{current-time-string}, accept a more-general @dfn{time value}
+format, which can be a list of integers as above, or a single number
+for seconds since the epoch, or @code{nil} for the current time.  You
+can convert a time value into a human-readable string using
+@code{current-time-string} and @code{format-time-string}, into a list
+of integers using @code{seconds-to-time}, and into other forms using
+@code{decode-time} and @code{float-time}.  These functions are
+described in the following sections.
 
 @defun current-time-string &optional time-value
 This function returns the current time and date as a human-readable
@@ -1256,8 +1253,8 @@ characters from the beginning of the string rather than from the end,
 as the year might not have exactly four digits, and additional
 information may some day be added at the end.
 
-The argument @var{time-value}, if given, specifies a time to format
-(represented as a list of integers), instead of the current time.
+The argument @var{time-value}, if given, specifies a time to format,
+instead of the current time.
 
 @example
 @group
@@ -1279,11 +1276,19 @@ become available.
 @defun float-time &optional time-value
 This function returns the current time as a floating-point number of
 seconds since the epoch.  The optional argument @var{time-value}, if
-given, specifies a time (represented as a list of integers) to convert
-instead of the current time.
+given, specifies a time to convert instead of the current time.
 
 @emph{Warning}: Since the result is floating point, it may not be
 exact.  Do not use this function if precise time stamps are required.
+
+@code{time-to-seconds} is an alias for this function.
+@end defun
+
+@defun seconds-to-time time-value
+This function converts a time value to list-of-integer form.
+For example, if @var{time-value} is a number, @code{(time-to-seconds
+(seconds-to-time @var{time-value}))} equals the number unless overflow
+or rounding errors occur.
 @end defun
 
 @defun current-time-zone &optional time-value
@@ -1302,8 +1307,8 @@ adjustment, then the value is constant through time.
 If the operating system doesn't supply all the information necessary to
 compute the value, the unknown elements of the list are @code{nil}.
 
-The argument @var{time-value}, if given, specifies a time (represented
-as a list of integers) to analyze instead of the current time.
+The argument @var{time-value}, if given, specifies a time value to
+analyze instead of the current time.
 @end defun
 
 The current time zone is determined by the @env{TZ} environment
@@ -1316,15 +1321,15 @@ time zone.
 @section Time Conversion
 @cindex calendrical information
 
-  These functions convert time values (lists of two to four integers,
-as explained in the previous section) into calendrical information and
-vice versa.
+  These functions convert time values (@pxref{Time of Day}) into
+calendrical information and vice versa.
 
-  Many 32-bit operating systems are limited to time values containing
-32 bits of information; these systems typically handle only the times
-from 1901-12-13 20:45:52 UTC through 2038-01-19 03:14:07 UTC@.
-However, 64-bit and some 32-bit operating systems have larger time
-values, and can represent times far in the past or future.
+  Many 32-bit operating systems are limited to system times containing
+32 bits of information in their seconds component; these systems
+typically handle only the times from 1901-12-13 20:45:52 UTC through
+2038-01-19 03:14:07 UTC@.  However, 64-bit and some 32-bit operating
+systems have larger seconds components, and can represent times far in
+the past or future.
 
   Time conversion functions always use the Gregorian calendar, even
 for dates before the Gregorian calendar was introduced.  Year numbers
@@ -1332,9 +1337,9 @@ count the number of years since the year 1 B.C., and do not skip zero
 as traditional Gregorian years do; for example, the year number
 @minus{}37 represents the Gregorian year 38 B.C@.
 
-@defun decode-time &optional time
+@defun decode-time &optional time-value
 This function converts a time value into calendrical information.  If
-you don't specify @var{time}, it decodes the current time.  The return
+you don't specify @var{time-value}, it decodes the current time.  The return
 value is a list of nine elements, as follows:
 
 @example
@@ -1373,8 +1378,9 @@ Greenwich.
 
 @defun encode-time seconds minutes hour day month year &optional zone
 This function is the inverse of @code{decode-time}.  It converts seven
-items of calendrical data into a time value.  For the meanings of the
-arguments, see the table above under @code{decode-time}.
+items of calendrical data into a list-of-integer time value.  For the
+meanings of the arguments, see the table above under
+@code{decode-time}.
 
 Year numbers less than 100 are not treated specially.  If you want them
 to stand for years above 1900, or years above 2000, you must alter them
@@ -1418,9 +1424,11 @@ This function parses the time-string @var{string} and returns the
 corresponding time value.
 @end defun
 
-@defun format-time-string format-string &optional time universal
-This function converts @var{time} (or the current time, if @var{time} is
-omitted) to a string according to @var{format-string}.  The argument
+@defun format-time-string format-string &optional time-value universal
+
+This function converts @var{time-value} (or the current time, if
+@var{time-value} is omitted) to a string according to
+@var{format-string}.  The argument
 @var{format-string} may contain @samp{%}-sequences which say to
 substitute parts of the time.  Here is a table of what the
 @samp{%}-sequences mean:
@@ -1540,12 +1548,6 @@ specified by @code{locale-coding-system} (@pxref{Locales}); after
 system.
 @end defun
 
-@defun seconds-to-time seconds
-This function converts @var{seconds}, the number of seconds since the
-epoch, to a time value and returns that.  To convert back, use
-@code{float-time} (@pxref{Time of Day}).
-@end defun
-
 @defun format-seconds format-string seconds
 This function converts its argument @var{seconds} into a string of
 years, days, hours, etc., according to @var{format-string}.  The
@@ -1619,7 +1621,7 @@ When called interactively, it prints the uptime in the echo area.
 
 @defun get-internal-run-time
 This function returns the processor run time used by Emacs as a list
-of four integers: @code{(@var{high} @var{low} @var{microsec}
+of four integers: @code{(@var{sec-high} @var{sec-low} @var{microsec}
 @var{picosec})}, using the same format as @code{current-time}
 (@pxref{Time of Day}).
 
@@ -1643,7 +1645,7 @@ interactively, it prints the duration in the echo area.
 @section Time Calculations
 
   These functions perform calendrical computations using time values
-(the kind of list that @code{current-time} returns).
+(@pxref{Time of Day}).
 
 @defun time-less-p t1 t2
 This returns @code{t} if time value @var{t1} is less than time value
@@ -1652,26 +1654,26 @@ This returns @code{t} if time value @var{t1} is less than time value
 
 @defun time-subtract t1 t2
 This returns the time difference @var{t1} @minus{} @var{t2} between
-two time values, in the same format as a time value.
+two time values, as a time value.
 @end defun
 
 @defun time-add t1 t2
-This returns the sum of two time values, one of which ought to
-represent a time difference rather than a point in time.
+This returns the sum of two time values, as a time value.
+One argument should represent a time difference rather than a point in time.
 Here is how to add a number of seconds to a time value:
 
 @example
-(time-add @var{time} (seconds-to-time @var{seconds}))
+(time-add @var{time} @var{seconds})
 @end example
 @end defun
 
-@defun time-to-days time
+@defun time-to-days time-value
 This function returns the number of days between the beginning of year
-1 and @var{time}.
+1 and @var{time-value}.
 @end defun
 
-@defun time-to-day-in-year time
-This returns the day number within the year corresponding to @var{time}.
+@defun time-to-day-in-year time-value
+This returns the day number within the year corresponding to @var{time-value}.
 @end defun
 
 @defun date-leap-year-p year
@@ -1915,8 +1917,7 @@ idleness.  Here's an example:
           (run-with-idle-timer
             ;; Compute an idle time @var{break-length}
             ;; more than the current value.
-            (time-add (current-idle-time)
-                      (seconds-to-time @var{break-length}))
+            (time-add (current-idle-time) @var{break-length})
             nil
             'my-timer-function))))
 @end example
diff --git a/etc/ChangeLog b/etc/ChangeLog
index 983fcaa28eb..ed8c345eef5 100644
--- a/etc/ChangeLog
+++ b/etc/ChangeLog
@@ -1,3 +1,8 @@
+2014-11-17  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Improve time stamp handling, and be more consistent about it.
+        * NEWS: Document the changes.
+
 2014-11-14  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * NEWS: Mention the new `M-s M-s' keystroke.
diff --git a/etc/NEWS b/etc/NEWS
index b0e08d46819..cb34e9b4613 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -377,6 +377,25 @@ optional repeat-count argument.
 *** New macros `thread-first' and `thread-last' allow threading a form
     as the first or last argument of subsequent forms.
 
++++
+** Time-related changes:
+
+*** Time-related functions now consistently accept numbers
+(representing seconds since the epoch) and nil (representing the
+current time) as well as the usual list-of-integer representation.
+Affected functions include `current-time-string', `current-time-zone',
+`decode-time', `float-time', `format-time-string', `seconds-to-time',
+`time-add', `time-less-p', `time-subtract', `time-to-day-in-year',
+`time-to-days', and `time-to-seconds'.
+
+*** The `encode-time-value' and `with-decoded-time-value' macros have
+been obsoleted.
+
+*** `calendar-next-time-zone-transition', `time-add', and
+`time-subtract' no longer return time values in the obsolete and
+undocumented integer-pair format.  Instead, they return a list of two
+integers.
+
 
 * Changes in Frames and Windows Code in Emacs 25.1
 
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index 7659d3c2235..7e516b95c61 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,31 @@
+2014-11-17  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Improve time stamp handling, and be more consistent about it.
+        This implements a suggestion made in:
+        http://lists.gnu.org/archive/html/emacs-devel/2014-10/msg00587.html
+        Among other things, this means timer.el no longer needs to
+        autoload the time-date module.
+        * allout-widgets.el (allout-elapsed-time-seconds): Doc fix.
+        * arc-mode.el (archive-ar-summarize):
+        * calendar/time-date.el (seconds-to-time, days-to-time, time-since):
+        * emacs-lisp/timer.el (timer-relative-time, timer-event-handler)
+        (run-at-time, with-timeout-suspend, with-timeout-unsuspend):
+        * net/tramp.el (tramp-time-less-p, tramp-time-subtract):
+        * proced.el (proced-time-lessp):
+        * timezone.el (timezone-time-from-absolute):
+        * type-break.el (type-break-schedule, type-break-time-sum):
+        Simplify by using new functionality.
+        * calendar/cal-dst.el (calendar-next-time-zone-transition):
+        Do not return time values in obsolete and undocumented (HI . LO)
+        format; use (HI LO) instead.
+        * calendar/time-date.el (with-decoded-time-value):
+        Treat 'nil' as current time.  This is mostly for XEmacs.
+        (encode-time-value, with-decoded-time-value): Obsolete.
+        (time-add, time-subtract, time-less-p): Use no-op autoloads, for
+        XEmacs.  Define only if XEmacs, as they're now C builtins in Emacs.
+        * ldefs-boot.el: Update to match new time-date.el
+        * proced.el: Do not require time-date.
+
 2014-11-16  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * net/eww.el (eww-mode): Make the buffer read-only.
diff --git a/lisp/allout-widgets.el b/lisp/allout-widgets.el
index f2dcdb40425..25abf3f9252 100644
--- a/lisp/allout-widgets.el
+++ b/lisp/allout-widgets.el
@@ -2342,9 +2342,9 @@ We use a caching strategy, so the caller doesn't need to do so."
       got)))
 
 ;;;_ : Miscellaneous
-;;;_  > allout-elapsed-time-seconds (triple)
+;;;_  > allout-elapsed-time-seconds (time-value time-value)
 (defun allout-elapsed-time-seconds (end start)
-  "Return seconds between `current-time' style time START/END triples."
+  "Return seconds between START/END time values."
   (let ((elapsed (time-subtract end start)))
     (float-time elapsed)))
 ;;;_  > allout-frame-property (frame property)
diff --git a/lisp/arc-mode.el b/lisp/arc-mode.el
index ef155ee2b99..a9f0ec71b51 100644
--- a/lisp/arc-mode.el
+++ b/lisp/arc-mode.el
@@ -2181,11 +2181,7 @@ This doesn't recover lost files, it just undoes changes in the buffer itself."
             (size (string-to-number (match-string 6))))
         ;; Move to the beginning of the data.
         (goto-char (match-end 0))
-        (setq time
-              (format-time-string
-               "%Y-%m-%d %H:%M"
-               (let ((high (truncate (/ time 65536))))
-                 (list high (truncate (- time (* 65536.0 high)))))))
+        (setq time (format-time-string "%Y-%m-%d %H:%M" time))
         (setq extname
               (cond ((equal name "//              ")
                      (propertize ".<ExtNamesTable>." 'face 'italic))
diff --git a/lisp/calendar/cal-dst.el b/lisp/calendar/cal-dst.el
index e3cb690306e..2a9cdee301d 100644
--- a/lisp/calendar/cal-dst.el
+++ b/lisp/calendar/cal-dst.el
@@ -179,6 +179,7 @@ Return nil if no such transition can be found."
          (if (eq (car (current-time-zone probe)) hi-utc-diff)
              (setq hi probe)
            (setq lo probe)))
+       (setcdr hi (list (cdr hi)))
        hi))))
 
 (autoload 'calendar-persian-to-absolute "cal-persia")
diff --git a/lisp/calendar/time-date.el b/lisp/calendar/time-date.el
index 82bc05f299f..100e856469a 100644
--- a/lisp/calendar/time-date.el
+++ b/lisp/calendar/time-date.el
@@ -30,10 +30,9 @@
 ;; value equal to HIGH * 2^16 + LOW + USEC * 10^-6 + PSEC * 10^-12
 ;; seconds, where missing components are treated as zero.  HIGH can be
 ;; negative, either because the value is a time difference, or because
-;; the machine supports negative time stamps that fall before the epoch.
-;; The macro `with-decoded-time-value' and the function
-;; `encode-time-value' make it easier to deal with these formats.
-;; See `time-subtract' for an example of how to use them.
+;; it represents a time stamp before the epoch.  Typically, there are
+;; more time values than the underlying system time type supports,
+;; but the reverse can also be true.
 
 ;;; Code:
 
@@ -71,6 +70,7 @@ list (HIGH LOW MICRO PICO)."
                           ,low ,micro)
                         (when pico `(,pico))
                         (when type `(,type)))
+           (or ,gensym (setq ,gensym (current-time)))
            (if (consp ,gensym)
                (progn
                  (setq ,low (pop ,gensym))
@@ -108,6 +108,10 @@ it is assumed that PICO was omitted and should be treated as zero."
    ((eq type 3) (list high low micro pico))
    ((null type) (encode-time-value high low micro 0 pico))))
 
+(when (featurep 'emacs)
+  (make-obsolete 'encode-time-value nil "25.1")
+  (make-obsolete 'with-decoded-time-value nil "25.1"))
+
 (autoload 'parse-time-string "parse-time")
 (autoload 'timezone-make-date-arpa-standard "timezone")
 
@@ -158,47 +162,17 @@ TIME defaults to the current time."
 
 ;;;###autoload
 (defun seconds-to-time (seconds)
-  "Convert SECONDS (a floating point number) to a time value."
-  (let* ((usec (* 1000000 (mod seconds 1)))
-         (ps (round (* 1000000 (mod usec 1))))
-         (us (floor usec))
-         (lo (floor (mod seconds 65536)))
-         (hi (floor seconds 65536)))
-    (if (eq ps 1000000)
-        (progn
-          (setq ps 0)
-          (setq us (1+ us))
-          (if (eq us 1000000)
-              (progn
-                (setq us 0)
-                (setq lo (1+ lo))
-                (if (eq lo 65536)
-                    (progn
-                      (setq lo 0)
-                      (setq hi (1+ hi))))))))
-    (list hi lo us ps)))
-
-;;;###autoload
-(defun time-less-p (t1 t2)
-  "Return non-nil if time value T1 is earlier than time value T2."
-  (with-decoded-time-value ((high1 low1 micro1 pico1 type1 t1)
-                            (high2 low2 micro2 pico2 type2 t2))
-    (or (< high1 high2)
-        (and (= high1 high2)
-             (or (< low1 low2)
-                 (and (= low1 low2)
-                      (or (< micro1 micro2)
-                          (and (= micro1 micro2)
-                               (< pico1 pico2)))))))))
+  "Convert SECONDS to a time value."
+  (time-add 0 seconds))
 
 ;;;###autoload
 (defun days-to-time (days)
   "Convert DAYS into a time value."
-  (let* ((seconds (* 1.0 days 60 60 24))
-         (high (condition-case nil (floor (/ seconds 65536))
-                 (range-error most-positive-fixnum))))
-    (list high (condition-case nil (floor (- seconds (* 1.0 high 65536)))
-                 (range-error 65535)))))
+  (let ((time (condition-case nil (seconds-to-time (* 86400.0 days))
+                (range-error (list most-positive-fixnum 65535)))))
+    (if (integerp days)
+        (setcdr (cdr time) nil))
+    time))
 
 ;;;###autoload
 (defun time-since (time)
@@ -207,53 +181,71 @@ TIME should be either a time value or a date-time string."
   (when (stringp time)
     ;; Convert date strings to internal time.
     (setq time (date-to-time time)))
-  (time-subtract (current-time) time))
+  (time-subtract nil time))
 
 ;;;###autoload
 (defalias 'subtract-time 'time-subtract)
 
-;;;###autoload
-(defun time-subtract (t1 t2)
-  "Subtract two time values, T1 minus T2.
-Return the difference in the format of a time value."
-  (with-decoded-time-value ((high low micro pico type t1)
-                            (high2 low2 micro2 pico2 type2 t2))
-    (setq high (- high high2)
-          low (- low low2)
-          micro (- micro micro2)
-          pico (- pico pico2)
-          type (max type type2))
-    (when (< pico 0)
-      (setq micro (1- micro)
-            pico (+ pico 1000000)))
-    (when (< micro 0)
-      (setq low (1- low)
-            micro (+ micro 1000000)))
-    (when (< low 0)
-      (setq high (1- high)
-            low (+ low 65536)))
-    (encode-time-value high low micro pico type)))
+;; These autoloads do nothing in Emacs 25, where the functions are builtin.
+;;;###autoload(autoload 'time-add "time-date")
+;;;###autoload(autoload 'time-subtract "time-date")
+;;;###autoload(autoload 'time-less-p "time-date")
 
-;;;###autoload
-(defun time-add (t1 t2)
-  "Add two time values T1 and T2.  One should represent a time difference."
-  (with-decoded-time-value ((high low micro pico type t1)
-                            (high2 low2 micro2 pico2 type2 t2))
-    (setq high (+ high high2)
-          low (+ low low2)
-          micro (+ micro micro2)
-          pico (+ pico pico2)
-          type (max type type2))
-    (when (>= pico 1000000)
-      (setq micro (1+ micro)
-            pico (- pico 1000000)))
-    (when (>= micro 1000000)
-      (setq low (1+ low)
-            micro (- micro 1000000)))
-    (when (>= low 65536)
-      (setq high (1+ high)
-            low (- low 65536)))
-    (encode-time-value high low micro pico type)))
+(eval-when-compile
+  (when (not (featurep 'emacs))
+
+    (defun time-add (t1 t2)
+      "Add two time values T1 and T2.  One should represent a time difference."
+      (with-decoded-time-value ((high low micro pico type t1)
+                                (high2 low2 micro2 pico2 type2 t2))
+        (setq high (+ high high2)
+              low (+ low low2)
+              micro (+ micro micro2)
+              pico (+ pico pico2)
+              type (max type type2))
+        (when (>= pico 1000000)
+          (setq micro (1+ micro)
+                pico (- pico 1000000)))
+        (when (>= micro 1000000)
+          (setq low (1+ low)
+                micro (- micro 1000000)))
+        (when (>= low 65536)
+          (setq high (1+ high)
+                low (- low 65536)))
+        (encode-time-value high low micro pico type)))
+
+    (defun time-subtract (t1 t2)
+      "Subtract two time values, T1 minus T2.
+Return the difference in the format of a time value."
+      (with-decoded-time-value ((high low micro pico type t1)
+                                (high2 low2 micro2 pico2 type2 t2))
+        (setq high (- high high2)
+              low (- low low2)
+              micro (- micro micro2)
+              pico (- pico pico2)
+              type (max type type2))
+        (when (< pico 0)
+          (setq micro (1- micro)
+                pico (+ pico 1000000)))
+        (when (< micro 0)
+          (setq low (1- low)
+                micro (+ micro 1000000)))
+        (when (< low 0)
+          (setq high (1- high)
+                low (+ low 65536)))
+        (encode-time-value high low micro pico type)))
+
+    (defun time-less-p (t1 t2)
+      "Return non-nil if time value T1 is earlier than time value T2."
+      (with-decoded-time-value ((high1 low1 micro1 pico1 type1 t1)
+                                (high2 low2 micro2 pico2 type2 t2))
+        (or (< high1 high2)
+            (and (= high1 high2)
+                 (or (< low1 low2)
+                     (and (= low1 low2)
+                          (or (< micro1 micro2)
+                              (and (= micro1 micro2)
+                                   (< pico1 pico2)))))))))))
 
 ;;;###autoload
 (defun date-to-day (date)
diff --git a/lisp/emacs-lisp/timer.el b/lisp/emacs-lisp/timer.el
index 7fc6bf7b920..a189d242ac4 100644
--- a/lisp/emacs-lisp/timer.el
+++ b/lisp/emacs-lisp/timer.el
@@ -125,9 +125,7 @@ of SECS seconds since the epoch.  SECS may be a fraction."
   "Advance TIME by SECS seconds and optionally USECS microseconds
 and PSECS picoseconds.  SECS may be either an integer or a
 floating point number."
-  (let ((delta (if (floatp secs)
-                   (seconds-to-time secs)
-                 (list (floor secs 65536) (mod secs 65536)))))
+  (let ((delta secs))
     (if (or usecs psecs)
         (setq delta (time-add delta (list 0 0 (or usecs 0) (or psecs 0)))))
     (time-add time delta)))
@@ -307,8 +305,8 @@ This function is called, by name, directly by the C code."
               ;; perhaps because Emacs was suspended for a long time,
               ;; limit how many times things get repeated.
               (if (and (numberp timer-max-repeats)
-                       (< 0 (timer-until timer (current-time))))
-                  (let ((repeats (/ (timer-until timer (current-time))
+                       (< 0 (timer-until timer nil)))
+                  (let ((repeats (/ (timer-until timer nil)
                                     (timer--repeat-delay timer))))
                     (if (> repeats timer-max-repeats)
                         (timer-inc-time timer (* (timer--repeat-delay timer)
@@ -374,13 +372,13 @@ This function returns a timer object which you can use in `cancel-timer'."
 
   ;; Handle numbers as relative times in seconds.
   (if (numberp time)
-      (setq time (timer-relative-time (current-time) time)))
+      (setq time (timer-relative-time nil time)))
 
   ;; Handle relative times like "2 hours 35 minutes"
   (if (stringp time)
       (let ((secs (timer-duration time)))
         (if secs
-            (setq time (timer-relative-time (current-time) secs)))))
+            (setq time (timer-relative-time nil secs)))))
 
   ;; Handle "11:23pm" and the like.  Interpret it as meaning today
   ;; which admittedly is rather stupid if we have passed that time
@@ -486,7 +484,7 @@ The value is a list that the debugger can pass to `with-timeout-unsuspend'
 when it exits, to make these timers start counting again."
   (mapcar (lambda (timer)
             (cancel-timer timer)
-            (list timer (time-subtract (timer--time timer) (current-time))))
+            (list timer (time-subtract (timer--time timer) nil)))
           with-timeout-timers))
 
 (defun with-timeout-unsuspend (timer-spec-list)
@@ -495,7 +493,7 @@ The argument should be a value previously returned by `with-timeout-suspend'."
   (dolist (elt timer-spec-list)
     (let ((timer (car elt))
           (delay (cadr elt)))
-      (timer-set-time timer (time-add (current-time) delay))
+      (timer-set-time timer (time-add nil delay))
       (timer-activate timer))))
 
 (defun y-or-n-p-with-timeout (prompt seconds default-value)
diff --git a/lisp/ldefs-boot.el b/lisp/ldefs-boot.el
index b78c906b450..f60d6608f7e 100644
--- a/lisp/ldefs-boot.el
+++ b/lisp/ldefs-boot.el
@@ -27478,15 +27478,10 @@ If DATE lacks timezone information, GMT is assumed.
  (autoload 'time-to-seconds "time-date"))
 
 (autoload 'seconds-to-time "time-date" "\
-Convert SECONDS (a floating point number) to a time value.
+Convert SECONDS to a time value.
 
 \(fn SECONDS)" nil nil)
 
-(autoload 'time-less-p "time-date" "\
-Return non-nil if time value T1 is earlier than time value T2.
-
-\(fn T1 T2)" nil nil)
-
 (autoload 'days-to-time "time-date" "\
 Convert DAYS into a time value.
 
@@ -27499,17 +27494,9 @@ TIME should be either a time value or a date-time string.
 \(fn TIME)" nil nil)
 
 (defalias 'subtract-time 'time-subtract)
-
-(autoload 'time-subtract "time-date" "\
-Subtract two time values, T1 minus T2.
-Return the difference in the format of a time value.
-
-\(fn T1 T2)" nil nil)
-
-(autoload 'time-add "time-date" "\
-Add two time values T1 and T2.  One should represent a time difference.
-
-\(fn T1 T2)" nil nil)
+(autoload 'time-add "time-date")
+(autoload 'time-subtract "time-date")
+(autoload 'time-less-p "time-date")
 
 (autoload 'date-to-day "time-date" "\
 Return the number of days between year 1 and DATE.
diff --git a/lisp/net/tramp.el b/lisp/net/tramp.el
index 5889743e28b..01cd8191169 100644
--- a/lisp/net/tramp.el
+++ b/lisp/net/tramp.el
@@ -4236,25 +4236,15 @@ Invokes `password-read' if available, `read-passwd' else."
     ("oct" . 10) ("nov" . 11) ("dec" . 12))
   "Alist mapping month names to integers.")
 
-;; FIXME: Shouldn't this also look at any subseconds parts of T1 and T2?
 ;;;###tramp-autoload
 (defun tramp-time-less-p (t1 t2)
   "Say whether time value T1 is less than time value T2."
-  (unless t1 (setq t1 '(0 0)))
-  (unless t2 (setq t2 '(0 0)))
-  (or (< (car t1) (car t2))
-      (and (= (car t1) (car t2))
-           (< (nth 1 t1) (nth 1 t2)))))
+  (time-less-p (or t1 0) (or t2 0)))
 
-;; FIXME: Shouldn't this also look at any subseconds parts of T1 and T2?
 (defun tramp-time-subtract (t1 t2)
   "Subtract two time values.
 Return the difference in the format of a time value."
-  (unless t1 (setq t1 '(0 0)))
-  (unless t2 (setq t2 '(0 0)))
-  (let ((borrow (< (cadr t1) (cadr t2))))
-    (list (- (car t1) (car t2) (if borrow 1 0))
-          (- (+ (if borrow 65536 0) (cadr t1)) (cadr t2)))))
+  (time-subtract (or t1 0) (or t2 0)))
 
 ;;;###tramp-autoload
 (defun tramp-time-diff (t1 t2)
diff --git a/lisp/proced.el b/lisp/proced.el
index 592c0d066c7..188b8c354c6 100644
--- a/lisp/proced.el
+++ b/lisp/proced.el
@@ -49,8 +49,6 @@
 
 ;;; Code:
 
-(require 'time-date)                 ; for `with-decoded-time-value'
-
 (defgroup proced nil
   "Proced mode."
   :group 'processes
@@ -1186,17 +1184,8 @@ Return nil otherwise."
 (defun proced-time-lessp (t1 t2)
   "Return t if time value T1 is less than time value T2.
 Return `equal' if T1 equals T2.  Return nil otherwise."
-  (with-decoded-time-value ((high1 low1 micro1 pico1 type1 t1)
-                            (high2 low2 micro2 pico2 type2 t2))
-    (cond ((< high1 high2))
-          ((< high2 high1) nil)
-          ((< low1 low2))
-          ((< low2 low1) nil)
-          ((< micro1 micro2))
-          ((< micro2 micro1) nil)
-          ((< pico1 pico2))
-          ((< pico2 pico1) nil)
-          (t 'equal))))
+  (or (time-less-p t1 t2)
+      (if (not (time-less-p t2 t1)) 'equal)))
 
 ;;; Sorting
 
diff --git a/lisp/timezone.el b/lisp/timezone.el
index 1135092b039..8ff43966f69 100644
--- a/lisp/timezone.el
+++ b/lisp/timezone.el
@@ -295,13 +295,9 @@ Gregorian date Sunday, December 31, 1 BC."
             ;; (timezone-absolute-from-gregorian 1 1 1970)
          (days (- date current-time-origin))
          (seconds-per-day (float 86400))
-         (seconds (+ seconds (* days seconds-per-day)))
-         (current-time-arithmetic-base (float 65536))
-         (hi (floor (/ seconds current-time-arithmetic-base)))
-         (hibase (* hi current-time-arithmetic-base))
-         (lo (floor (- seconds hibase))))
-     (and (< (abs (- seconds (+ hibase lo))) 2) ;; Check for integer overflow.
-          (cons hi lo))))
+         (day-seconds (* days seconds-per-day)))
+    (condition-case nil (time-add day-seconds seconds)
+      (range-error))))
 
 (defun timezone-time-zone-from-absolute (date seconds)
   "Compute the local time zone for DATE at time SECONDS after midnight.
diff --git a/lisp/type-break.el b/lisp/type-break.el
index f954e5d1c26..a3af407bf17 100644
--- a/lisp/type-break.el
+++ b/lisp/type-break.el
@@ -604,8 +604,7 @@ INTERVAL is the full length of an interval (defaults to TIME)."
   (type-break-time-warning-schedule time 'reset)
   (type-break-run-at-time (max 1 time) nil 'type-break-alarm)
   (setq type-break-time-next-break
-        (type-break-time-sum (or start (current-time))
-                             (or interval time))))
+        (type-break-time-sum start (or interval time))))
 
 (defun type-break-cancel-schedule ()
   (type-break-cancel-time-warning-schedule)
@@ -961,19 +960,11 @@ FRAC should be the inverse of the fractional value; for example, a value of
 (defun type-break-time-difference (a b)
   (round (float-time (time-subtract b a))))
 
-;; Return (in a new list the same in structure to that returned by
-;; `current-time') the sum of the arguments.  Each argument may be a time
-;; list or a single integer, a number of seconds.
-;; This function keeps the high and low 16 bits of the seconds properly
-;; balanced so that the lower value never exceeds 16 bits.  Otherwise, when
-;; the result is passed to `current-time-string' it will toss some of the
-;; "low" bits and format the time incorrectly.
+;; Return a time value that is the sum of the time-value arguments.
 (defun type-break-time-sum (&rest tmlist)
-  (let ((sum '(0 0 0)))
+  (let ((sum '(0 0)))
     (dolist (tem tmlist)
-      (setq sum (time-add sum (if (integerp tem)
-                                  (list (floor tem 65536) (mod tem 65536))
-                                tem))))
+      (setq sum (time-add sum tem)))
     sum))
 
 (defun type-break-time-stamp (&optional when)
diff --git a/src/ChangeLog b/src/ChangeLog
index d1888987dbc..b169479a274 100644
--- a/src/ChangeLog
+++ b/src/ChangeLog
@@ -1,3 +1,31 @@
+2014-11-17  Paul Eggert  <eggert@cs.ucla.edu>
+
+        Improve time stamp handling, and be more consistent about it.
+        * editfns.c (invalid_time): New function.
+        Use it instead of 'error ("Invalid time specification")'.
+        (time_add, time_subtract, time_arith, Ftime_add, Ftime_less_p)
+        (decode_float_time, lisp_to_timespec, lisp_time_struct):
+        New functions.
+        (make_time_tail, make_time): Remove.  All uses changed to use
+        new functions or plain list4i.
+        (disassemble_lisp_time): Return effective length if successful.
+        Check that LOW is an integer, if it's combined with other components.
+        (decode_time_components): Decode into struct lisp_time, not
+        struct timespec, so that we can support a wide set of times
+        regardless of whether time_t is signed.  Decode plain numbers
+        as seconds since the Epoch, and nil as the current time.
+        (lisp_time_argument, lisp_seconds_argument, Ffloat_time):
+        Reimplement in terms of new functions.
+        (Fencode_time): Just use list2i.
+        (syms_of_editfns): Add time-add, time-subtract, time-less-p.
+        * keyboard.c (decode_timer): Don't allow the new formats (floating
+        point or nil) in timers.
+        * systime.h (LO_TIME_BITS): New constant.  Use it everywhere in
+        place of the magic number '16'.
+        (struct lisp_time): New type.
+        (decode_time_components): Use it.
+        (lisp_to_timespec): New decl.
+
 2014-11-16  Lars Magne Ingebrigtsen  <larsi@gnus.org>
 
         * intervals.h (INTERVAL_WRITABLE_P): Check the `inhibit-read-only'
diff --git a/src/editfns.c b/src/editfns.c
index 376d8e3a0ea..0a07886934c 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -64,6 +64,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 extern Lisp_Object w32_get_internal_run_time (void);
 #endif
 
+static struct lisp_time lisp_time_struct (Lisp_Object, int *);
 static void set_time_zone_rule (char const *);
 static Lisp_Object format_time_string (char const *, ptrdiff_t, struct timespec,
                                        bool, struct tm *);
@@ -1392,6 +1393,12 @@ time_overflow (void)
   error ("Specified time is not representable");
 }
 
+static void
+invalid_time (void)
+{
+  error ("Invalid time specification");
+}
+
 /* A substitute for mktime_z on platforms that lack it.  It's not
    thread-safe, but should be good enough for Emacs in typical use.  */
 #ifndef HAVE_TZALLOC
@@ -1420,26 +1427,26 @@ mktime_z (timezone_t tz, struct tm *tm)
 static EMACS_INT
 hi_time (time_t t)
 {
-  time_t hi = t >> 16;
+  time_t hi = t >> LO_TIME_BITS;
 
   /* Check for overflow, helping the compiler for common cases where
      no runtime check is needed, and taking care not to convert
      negative numbers to unsigned before comparing them.  */
   if (! ((! TYPE_SIGNED (time_t)
-          || MOST_NEGATIVE_FIXNUM <= TIME_T_MIN >> 16
+          || MOST_NEGATIVE_FIXNUM <= TIME_T_MIN >> LO_TIME_BITS
           || MOST_NEGATIVE_FIXNUM <= hi)
-         && (TIME_T_MAX >> 16 <= MOST_POSITIVE_FIXNUM
+         && (TIME_T_MAX >> LO_TIME_BITS <= MOST_POSITIVE_FIXNUM
              || hi <= MOST_POSITIVE_FIXNUM)))
     time_overflow ();
 
   return hi;
 }
 
-/* Return the bottom 16 bits of the time T.  */
+/* Return the bottom bits of the time T.  */
 static int
 lo_time (time_t t)
 {
-  return t & ((1 << 16) - 1);
+  return t & ((1 << LO_TIME_BITS) - 1);
 }
 
 DEFUN ("current-time", Fcurrent_time, Scurrent_time, 0, 0, 0,
@@ -1453,6 +1460,96 @@ picosecond counts.  */)
   return make_lisp_time (current_timespec ());
 }
 
+static struct lisp_time
+time_add (struct lisp_time ta, struct lisp_time tb)
+{
+  EMACS_INT hi = ta.hi + tb.hi;
+  int lo = ta.lo + tb.lo;
+  int us = ta.us + tb.us;
+  int ps = ta.ps + tb.ps;
+  us += (1000000 <= ps);
+  ps -= (1000000 <= ps) * 1000000;
+  lo += (1000000 <= us);
+  us -= (1000000 <= us) * 1000000;
+  hi += (1 << LO_TIME_BITS <= lo);
+  lo -= (1 << LO_TIME_BITS <= lo) << LO_TIME_BITS;
+  return (struct lisp_time) { hi, lo, us, ps };
+}
+
+static struct lisp_time
+time_subtract (struct lisp_time ta, struct lisp_time tb)
+{
+  EMACS_INT hi = ta.hi - tb.hi;
+  int lo = ta.lo - tb.lo;
+  int us = ta.us - tb.us;
+  int ps = ta.ps - tb.ps;
+  us -= (ps < 0);
+  ps += (ps < 0) * 1000000;
+  lo -= (us < 0);
+  us += (us < 0) * 1000000;
+  hi -= (lo < 0);
+  lo += (lo < 0) << LO_TIME_BITS;
+  return (struct lisp_time) { hi, lo, us, ps };
+}
+
+static Lisp_Object
+time_arith (Lisp_Object a, Lisp_Object b,
+            struct lisp_time (*op) (struct lisp_time, struct lisp_time))
+{
+  int alen, blen;
+  struct lisp_time ta = lisp_time_struct (a, &alen);
+  struct lisp_time tb = lisp_time_struct (b, &blen);
+  struct lisp_time t = op (ta, tb);
+  if (! (MOST_NEGATIVE_FIXNUM <= t.hi && t.hi <= MOST_POSITIVE_FIXNUM))
+    time_overflow ();
+  Lisp_Object val = Qnil;
+
+  switch (max (alen, blen))
+    {
+    default:
+      val = Fcons (make_number (t.ps), val);
+      /* Fall through.  */
+    case 3:
+      val = Fcons (make_number (t.us), val);
+      /* Fall through.  */
+    case 2:
+      val = Fcons (make_number (t.lo), val);
+      val = Fcons (make_number (t.hi), val);
+      break;
+    }
+
+  return val;
+}
+
+DEFUN ("time-add", Ftime_add, Stime_add, 2, 2, 0,
+       doc: /* Return the sum of two time values A and B, as a time value.  */)
+  (Lisp_Object a, Lisp_Object b)
+{
+  return time_arith (a, b, time_add);
+}
+
+DEFUN ("time-subtract", Ftime_subtract, Stime_subtract, 2, 2, 0,
+       doc: /* Return the difference between two time values A and B, as a time value.  */)
+  (Lisp_Object a, Lisp_Object b)
+{
+  return time_arith (a, b, time_subtract);
+}
+
+DEFUN ("time-less-p", Ftime_less_p, Stime_less_p, 2, 2, 0,
+       doc: /* Return non-nil if time value T1 is earlier than time value T2.  */)
+  (Lisp_Object t1, Lisp_Object t2)
+{
+  int t1len, t2len;
+  struct lisp_time a = lisp_time_struct (t1, &t1len);
+  struct lisp_time b = lisp_time_struct (t2, &t2len);
+  return ((a.hi != b.hi ? a.hi < b.hi
+           : a.lo != b.lo ? a.lo < b.lo
+           : a.us != b.us ? a.us < b.us
+           : a.ps < b.ps)
+          ? Qt : Qnil);
+}
+
+
 DEFUN ("get-internal-run-time", Fget_internal_run_time, Sget_internal_run_time,
        0, 0, 0,
        doc: /* Return the current run time used by Emacs.
@@ -1491,21 +1588,6 @@ does the same thing as `current-time'.  */)
 }
 
 
-/* Make a Lisp list that represents the time T with fraction TAIL.  */
-static Lisp_Object
-make_time_tail (time_t t, Lisp_Object tail)
-{
-  return Fcons (make_number (hi_time (t)),
-                Fcons (make_number (lo_time (t)), tail));
-}
-
-/* Make a Lisp list that represents the system time T.  */
-static Lisp_Object
-make_time (time_t t)
-{
-  return make_time_tail (t, Qnil);
-}
-
 /* Make a Lisp list that represents the Emacs time T.  T may be an
    invalid time, with a slightly negative tv_nsec value such as
    UNKNOWN_MODTIME_NSECS; in that case, the Lisp list contains a
@@ -1513,23 +1595,30 @@ make_time (time_t t)
 Lisp_Object
 make_lisp_time (struct timespec t)
 {
+  time_t s = t.tv_sec;
   int ns = t.tv_nsec;
-  return make_time_tail (t.tv_sec, list2i (ns / 1000, ns % 1000 * 1000));
+  return list4i (hi_time (s), lo_time (s), ns / 1000, ns % 1000 * 1000);
 }
 
 /* Decode a Lisp list SPECIFIED_TIME that represents a time.
    Set *PHIGH, *PLOW, *PUSEC, *PPSEC to its parts; do not check their values.
-   Return true if successful.  */
-static bool
+   Return 2, 3, or 4 to indicate the effective length of SPECIFIED_TIME
+   if successful, 0 if unsuccessful.  */
+static int
 disassemble_lisp_time (Lisp_Object specified_time, Lisp_Object *phigh,
                        Lisp_Object *plow, Lisp_Object *pusec,
                        Lisp_Object *ppsec)
 {
+  Lisp_Object high = make_number (0);
+  Lisp_Object low = specified_time;
+  Lisp_Object usec = make_number (0);
+  Lisp_Object psec = make_number (0);
+  int len = 4;
+
   if (CONSP (specified_time))
     {
-      Lisp_Object low = XCDR (specified_time);
-      Lisp_Object usec = make_number (0);
-      Lisp_Object psec = make_number (0);
+      high = XCAR (specified_time);
+      low = XCDR (specified_time);
       if (CONSP (low))
         {
           Lisp_Object low_tail = XCDR (low);
@@ -1540,40 +1629,119 @@ disassemble_lisp_time (Lisp_Object specified_time, Lisp_Object *phigh,
               low_tail = XCDR (low_tail);
               if (CONSP (low_tail))
                 psec = XCAR (low_tail);
+              else
+                len = 3;
             }
           else if (!NILP (low_tail))
-            usec = low_tail;
+            {
+              usec = low_tail;
+              len = 3;
+            }
+          else
+            len = 2;
         }
+      else
+        len = 2;
 
-      *phigh = XCAR (specified_time);
-      *plow = low;
-      *pusec = usec;
-      *ppsec = psec;
-      return 1;
+      /* When combining components, require LOW to be an integer,
+         as otherwise it would be a pain to add up times.  */
+      if (! INTEGERP (low))
+        return 0;
     }
+  else if (INTEGERP (specified_time))
+    len = 2;
+
+  *phigh = high;
+  *plow = low;
+  *pusec = usec;
+  *ppsec = psec;
+  return len;
+}
 
-  return 0;
+/* Convert T into an Emacs time *RESULT, truncating toward minus infinity.
+   Return true if T is in range, false otherwise.  */
+static bool
+decode_float_time (double t, struct lisp_time *result)
+{
+  double lo_multiplier = 1 << LO_TIME_BITS;
+  double emacs_time_min = MOST_NEGATIVE_FIXNUM * lo_multiplier;
+  if (! (emacs_time_min <= t && t < -emacs_time_min))
+    return false;
+
+  double small_t = t / lo_multiplier;
+  EMACS_INT hi = small_t;
+  double t_sans_hi = t - hi * lo_multiplier;
+  int lo = t_sans_hi;
+  long double fracps = (t_sans_hi - lo) * 1e12L;
+#ifdef INT_FAST64_MAX
+  int_fast64_t ifracps = fracps;
+  int us = ifracps / 1000000;
+  int ps = ifracps % 1000000;
+#else
+  int us = fracps / 1e6L;
+  int ps = fracps - us * 1e6L;
+#endif
+  us -= (ps < 0);
+  ps += (ps < 0) * 1000000;
+  lo -= (us < 0);
+  us += (us < 0) * 1000000;
+  hi -= (lo < 0);
+  lo += (lo < 0) << LO_TIME_BITS;
+  result->hi = hi;
+  result->lo = lo;
+  result->us = us;
+  result->ps = ps;
+  return true;
 }
 
 /* From the time components HIGH, LOW, USEC and PSEC taken from a Lisp
    list, generate the corresponding time value.
+   If LOW is floating point, the other components should be zero.
 
-   If RESULT is not null, store into *RESULT the converted time;
-   if the converted time does not fit into struct timespec,
-   store an invalid timespec to indicate the overflow.
+   If RESULT is not null, store into *RESULT the converted time.
    If *DRESULT is not null, store into *DRESULT the number of
    seconds since the start of the POSIX Epoch.
 
-   Return true if successful.  */
+   Return true if successful, false if the components are of the
+   wrong type or represent a time out of range.  */
 bool
 decode_time_components (Lisp_Object high, Lisp_Object low, Lisp_Object usec,
                         Lisp_Object psec,
-                        struct timespec *result, double *dresult)
+                        struct lisp_time *result, double *dresult)
 {
   EMACS_INT hi, lo, us, ps;
-  if (! (INTEGERP (high) && INTEGERP (low)
+  if (! (INTEGERP (high)
          && INTEGERP (usec) && INTEGERP (psec)))
     return false;
+  if (! INTEGERP (low))
+    {
+      if (FLOATP (low))
+        {
+          double t = XFLOAT_DATA (low);
+          if (result && ! decode_float_time (t, result))
+            return false;
+          if (dresult)
+            *dresult = t;
+          return true;
+        }
+      else if (NILP (low))
+        {
+          struct timespec now = current_timespec ();
+          if (result)
+            {
+              result->hi = hi_time (now.tv_sec);
+              result->lo = lo_time (now.tv_sec);
+              result->us = now.tv_nsec / 1000;
+              result->ps = now.tv_nsec % 1000 * 1000;
+            }
+          if (dresult)
+            *dresult = now.tv_sec + now.tv_nsec / 1e9;
+          return true;
+        }
+      else
+        return false;
+    }
+
   hi = XINT (high);
   lo = XINT (low);
   us = XINT (usec);
@@ -1583,53 +1751,68 @@ decode_time_components (Lisp_Object high, Lisp_Object low, Lisp_Object usec,
      each overflow into the next higher-order component.  */
   us += ps / 1000000 - (ps % 1000000 < 0);
   lo += us / 1000000 - (us % 1000000 < 0);
-  hi += lo >> 16;
+  hi += lo >> LO_TIME_BITS;
   ps = ps % 1000000 + 1000000 * (ps % 1000000 < 0);
   us = us % 1000000 + 1000000 * (us % 1000000 < 0);
-  lo &= (1 << 16) - 1;
+  lo &= (1 << LO_TIME_BITS) - 1;
 
   if (result)
     {
-      if ((TYPE_SIGNED (time_t) ? TIME_T_MIN >> 16 <= hi : 0 <= hi)
-          && hi <= TIME_T_MAX >> 16)
-        {
-          /* Return the greatest representable time that is not greater
-             than the requested time.  */
-          time_t sec = hi;
-          *result = make_timespec ((sec << 16) + lo, us * 1000 + ps / 1000);
-        }
-      else
-        *result = invalid_timespec ();
+      if (! (MOST_NEGATIVE_FIXNUM <= hi && hi <= MOST_POSITIVE_FIXNUM))
+        return false;
+      result->hi = hi;
+      result->lo = lo;
+      result->us = us;
+      result->ps = ps;
     }
 
   if (dresult)
-    *dresult = (us * 1e6 + ps) / 1e12 + lo + hi * 65536.0;
+    {
+      double dhi = hi;
+      *dresult = (us * 1e6 + ps) / 1e12 + lo + dhi * (1 << LO_TIME_BITS);
+    }
 
   return true;
 }
 
+struct timespec
+lisp_to_timespec (struct lisp_time t)
+{
+  if (! ((TYPE_SIGNED (time_t) ? TIME_T_MIN >> LO_TIME_BITS <= t.hi : 0 <= t.hi)
+         && t.hi <= TIME_T_MAX >> LO_TIME_BITS))
+    return invalid_timespec ();
+  time_t s = (t.hi << LO_TIME_BITS) + t.lo;
+  int ns = t.us * 1000 + t.ps / 1000;
+  return make_timespec (s, ns);
+}
+
 /* Decode a Lisp list SPECIFIED_TIME that represents a time.
+   Store its effective length into *PLEN.
    If SPECIFIED_TIME is nil, use the current time.
+   Signal an error if SPECIFIED_TIME does not represent a time.  */
+static struct lisp_time
+lisp_time_struct (Lisp_Object specified_time, int *plen)
+{
+  Lisp_Object high, low, usec, psec;
+  struct lisp_time t;
+  int len = disassemble_lisp_time (specified_time, &high, &low, &usec, &psec);
+  if (! (len && decode_time_components (high, low, usec, psec, &t, 0)))
+    invalid_time ();
+  *plen = len;
+  return t;
+}
 
-   Round the time down to the nearest struct timespec value.
-   Return seconds since the Epoch.
-   Signal an error if unsuccessful.  */
+/* Like lisp_time_struct, except return a struct timespec.
+   Discard any low-order digits.  */
 struct timespec
 lisp_time_argument (Lisp_Object specified_time)
 {
-  if (NILP (specified_time))
-    return current_timespec ();
-  else
-    {
-      Lisp_Object high, low, usec, psec;
-      struct timespec t;
-      if (! (disassemble_lisp_time (specified_time, &high, &low, &usec, &psec)
-             && decode_time_components (high, low, usec, psec, &t, 0)))
-        error ("Invalid time specification");
-      if (! timespec_valid_p (t))
-        time_overflow ();
-      return t;
-    }
+  int len;
+  struct lisp_time lt = lisp_time_struct (specified_time, &len);
+  struct timespec t = lisp_to_timespec (lt);
+  if (! timespec_valid_p (t))
+    time_overflow ();
+  return t;
 }
 
 /* Like lisp_time_argument, except decode only the seconds part,
@@ -1637,20 +1820,16 @@ lisp_time_argument (Lisp_Object specified_time)
 static time_t
 lisp_seconds_argument (Lisp_Object specified_time)
 {
-  if (NILP (specified_time))
-    return time (NULL);
-  else
-    {
-      Lisp_Object high, low, usec, psec;
-      struct timespec t;
-      if (! (disassemble_lisp_time (specified_time, &high, &low, &usec, &psec)
-             && decode_time_components (high, low, make_number (0),
-                                        make_number (0), &t, 0)))
-        error ("Invalid time specification");
-      if (! timespec_valid_p (t))
-        time_overflow ();
-      return t.tv_sec;
-    }
+  Lisp_Object high, low, usec, psec;
+  struct lisp_time t;
+  if (! (disassemble_lisp_time (specified_time, &high, &low, &usec, &psec)
+         && decode_time_components (high, low, make_number (0),
+                                    make_number (0), &t, 0)))
+    invalid_time ();
+  if (! ((TYPE_SIGNED (time_t) ? TIME_T_MIN >> LO_TIME_BITS <= t.hi : 0 <= t.hi)
+         && t.hi <= TIME_T_MAX >> LO_TIME_BITS))
+    time_overflow ();
+  return (t.hi << LO_TIME_BITS) + t.lo;
 }
 
 DEFUN ("float-time", Ffloat_time, Sfloat_time, 0, 1, 0,
@@ -1668,18 +1847,10 @@ or (if you need time as a string) `format-time-string'.  */)
   (Lisp_Object specified_time)
 {
   double t;
-  if (NILP (specified_time))
-    {
-      struct timespec now = current_timespec ();
-      t = now.tv_sec + now.tv_nsec / 1e9;
-    }
-  else
-    {
-      Lisp_Object high, low, usec, psec;
-      if (! (disassemble_lisp_time (specified_time, &high, &low, &usec, &psec)
-             && decode_time_components (high, low, usec, psec, 0, &t)))
-        error ("Invalid time specification");
-    }
+  Lisp_Object high, low, usec, psec;
+  if (! (disassemble_lisp_time (specified_time, &high, &low, &usec, &psec)
+         && decode_time_components (high, low, usec, psec, 0, &t)))
+    invalid_time ();
   return make_float (t);
 }
 
@@ -1969,7 +2140,7 @@ usage: (encode-time SECOND MINUTE HOUR DAY MONTH YEAR &optional ZONE)  */)
   if (value == (time_t) -1)
     time_overflow ();
 
-  return make_time (value);
+  return list2i (hi_time (value), lo_time (value));
 }
 
 DEFUN ("current-time-string", Fcurrent_time_string, Scurrent_time_string, 0, 1, 0,
@@ -4874,6 +5045,9 @@ functions if all the text being accessed has this property.  */);
   defsubr (&Suser_full_name);
   defsubr (&Semacs_pid);
   defsubr (&Scurrent_time);
+  defsubr (&Stime_add);
+  defsubr (&Stime_subtract);
+  defsubr (&Stime_less_p);
   defsubr (&Sget_internal_run_time);
   defsubr (&Sformat_time_string);
   defsubr (&Sfloat_time);
diff --git a/src/keyboard.c b/src/keyboard.c
index 060784cf0af..908eb59ff9c 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -4429,10 +4429,15 @@ decode_timer (Lisp_Object timer, struct timespec *result)
   vector = XVECTOR (timer)->contents;
   if (! NILP (vector[0]))
     return 0;
-
-  return (decode_time_components (vector[1], vector[2], vector[3], vector[8],
-                                  result, 0)
-          && timespec_valid_p (*result));
+  if (! INTEGERP (vector[2]))
+    return false;
+
+  struct lisp_time t;
+  if (! decode_time_components (vector[1], vector[2], vector[3], vector[8],
+                                &t, 0))
+    return false;
+  *result = lisp_to_timespec (t);
+  return timespec_valid_p (*result);
 }
 
 
diff --git a/src/systime.h b/src/systime.h
index 8f018044660..e0f7eec7977 100644
--- a/src/systime.h
+++ b/src/systime.h
@@ -86,10 +86,23 @@ extern void set_waiting_for_input (struct timespec *);
    happen when this files is used outside the src directory).
    Use GCPRO1 to determine if lisp.h was included.  */
 #ifdef GCPRO1
+
+/* Emacs uses the integer list (HI LO US PS) to represent the time
+   (HI << LO_TIME_BITS) + LO + US / 1e6 + PS / 1e12.  */
+enum { LO_TIME_BITS = 16 };
+
+/* A Lisp time (HI LO US PS), sans the cons cells.  */
+struct lisp_time
+{
+  EMACS_INT hi;
+  int lo, us, ps;
+};
+
 /* defined in editfns.c */
 extern Lisp_Object make_lisp_time (struct timespec);
 extern bool decode_time_components (Lisp_Object, Lisp_Object, Lisp_Object,
-                                    Lisp_Object, struct timespec *, double *);
+                                    Lisp_Object, struct lisp_time *, double *);
+extern struct timespec lisp_to_timespec (struct lisp_time);
 extern struct timespec lisp_time_argument (Lisp_Object);
 #endif