master 0ade20f: Calc: fix formatting and parsing Unix time (bug#43759)

[Mattias Engdegård]

branch: master
commit 0ade20f49f80d2d93f596ba9dfa3f1309ad84126
Author: Mattias Engdegård <mattiase@acm.org>
Commit: Mattias Engdegård <mattiase@acm.org>

    Calc: fix formatting and parsing Unix time (bug#43759)
    
    The number of days from epoch to Jan 1, 1970 that was used in parsing
    and formatting Unix time was incorrect.  The previous fix
    (in e368697ce36) was incomplete.
    
    Reported by Vincent Belaïche.
    
    * lisp/calc/calc-forms.el (math-unix-epoch): New constant.
    (math-format-date-part, math-parse-standard-date, calcFunc-unixtime):
    Use math-unix-epoch instead of a constant that is sometimes wrong.
    * test/lisp/calc/calc-tests.el (calc-unix-date): New test.
---
 lisp/calc/calc-forms.el      | 13 +++++++++----
 test/lisp/calc/calc-tests.el | 40 ++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/lisp/calc/calc-forms.el b/lisp/calc/calc-forms.el
index 6d70126..a2f6696 100644
--- a/lisp/calc/calc-forms.el
+++ b/lisp/calc/calc-forms.el
@@ -709,6 +709,10 @@ as measured in the number of days before December 31, 1 BC 
(Gregorian).")
   "The beginning of the Julian date calendar,
 as measured in the integer number of days before December 31, 1 BC 
(Gregorian).")
 
+(defconst math-unix-epoch 719163
+  "The beginning of Unix time: days from December 31, 1 BC (Gregorian)
+to Jan 1, 1970 AD.")
+
 (defun math-format-date-part (x)
   (cond ((stringp x)
         x)
@@ -730,7 +734,8 @@ as measured in the integer number of days before December 
31, 1 BC (Gregorian)."
                               (math-floor math-fd-date)
                               math-julian-date-beginning-int)))
        ((eq x 'U)
-        (math-format-number (nth 1 (math-date-parts math-fd-date 719164))))
+        (math-format-number (nth 1 (math-date-parts math-fd-date
+                                                     math-unix-epoch))))
         ((memq x '(IYYY Iww w))
          (progn
            (or math-fd-iso-dt
@@ -1173,7 +1178,7 @@ as measured in the integer number of days before December 
31, 1 BC (Gregorian)."
                      (setq num (math-match-substring math-pd-str 0)
                            math-pd-str (substring math-pd-str (match-end 0))
                            num (math-date-to-dt
-                                (math-add 719164
+                                (math-add math-unix-epoch
                                           (math-div (math-read-number num)
                                                     '(float 864 2))))
                            hour (nth 3 num)
@@ -1434,11 +1439,11 @@ as measured in the integer number of days before 
December 31, 1 BC (Gregorian)."
 (defun calcFunc-unixtime (date &optional zone)
   (if (math-realp date)
       (progn
-       (setq date (math-add 719163 (math-div date '(float 864 2))))
+       (setq date (math-add math-unix-epoch (math-div date '(float 864 2))))
        (list 'date (math-sub date (math-div (calcFunc-tzone zone date)
                                             '(float 864 2)))))
     (if (eq (car date) 'date)
-       (math-add (nth 1 (math-date-parts (nth 1 date) 719163))
+       (math-add (nth 1 (math-date-parts (nth 1 date) math-unix-epoch))
                  (calcFunc-tzone zone date))
       (math-reject-arg date 'datep))))
 
diff --git a/test/lisp/calc/calc-tests.el b/test/lisp/calc/calc-tests.el
index 4dded00..0df96a0 100644
--- a/test/lisp/calc/calc-tests.el
+++ b/test/lisp/calc/calc-tests.el
@@ -534,6 +534,46 @@ An existing calc stack is reused, otherwise a new one is 
created."
       )
   ))
 
+(ert-deftest calc-unix-date ()
+  (let* ((d-1970-01-01 (math-parse-date "1970-01-01"))
+         (d-2020-09-07 (math-parse-date "2020-09-07"))
+         (d-1991-01-09-0600 (math-parse-date "1991-01-09 06:00")))
+    ;; calcFunc-unixtime (command "t U") converts a date value to Unix time,
+    ;; and a number to a date.
+    (should (equal d-1970-01-01 '(date 719163)))
+    (should (equal (calcFunc-unixtime d-1970-01-01 0) 0))
+    (should (equal (calc-tests--calc-to-number (cadr (calcFunc-unixtime 0 0)))
+                   (cadr d-1970-01-01)))
+    (should (equal (calcFunc-unixtime d-2020-09-07 0)
+                   (* (- (cadr d-2020-09-07)
+                         (cadr d-1970-01-01))
+                      86400)))
+    (should (equal (calcFunc-unixtime d-1991-01-09-0600 0)
+                   663400800))
+    (should (equal (calc-tests--calc-to-number
+                    (cadr (calcFunc-unixtime 663400800 0)))
+                   726841.25))
+
+    (let ((calc-date-format '(U)))
+      ;; Test parsing Unix time.
+      (should (equal (calc-tests--calc-to-number
+                      (cadr (math-parse-date "0")))
+                     719163))
+      (should (equal (calc-tests--calc-to-number
+                      (cadr (math-parse-date "469324800")))
+                     (+ 719163 (/ 469324800 86400))))
+      (should (equal (calc-tests--calc-to-number
+                      (cadr (math-parse-date "663400800")))
+                     726841.25))
+
+      ;; Test formatting Unix time.
+      (should (equal (math-format-date d-1970-01-01) "0"))
+      (should (equal (math-format-date d-2020-09-07)
+                     (number-to-string (* (- (cadr d-2020-09-07)
+                                             (cadr d-1970-01-01))
+                                          86400))))
+      (should (equal (math-format-date d-1991-01-09-0600) "663400800")))))
+
 (provide 'calc-tests)
 ;;; calc-tests.el ends here