* bug#36822: 26.2; Calc: calc-julian produces incorrect result
2019-07-30 11:08 ` Mattias Engdegård
@ 2019-07-30 15:51 ` Mattias Engdegård
2019-08-06 12:04 ` Mattias Engdegård
0 siblings, 1 reply; 4+ messages in thread
From: Mattias Engdegård @ 2019-07-30 15:51 UTC (permalink / raw)
To: michel; +Cc: 36822
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tags 36822 patch
quit
> It looks like there are multiple flaws involved.
This was indeed the case. Attached is a patch that attempts to fix those that I found (I didn't dig very deeply).
As I'm no calendar expert, I would greatly value an independent review of the patch.
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From 0facfe8988f7d0614d8cce124a8a7cabaf7450ed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mattias=20Engdeg=C3=A5rd?= <mattiase@acm.org>
Date: Tue, 30 Jul 2019 17:33:19 +0200
Subject: [PATCH] Fix various Calc date conversions (bug#36822)
* lisp/calc/calc-forms.el (math-absolute-from-gregorian-dt):
Rewrite in a way that I understand, and that actually seems to work.
(math-absolute-from-julian-dt): Use Julian, not Gregorian, leap year
rules for counting days within a year.
(math-julian-date-beginning, math-julian-date-beginning-int):
Change constants to be consistent with their doc strings and the code:
use Rata Die epoch at Dec 31, 1 BC Gregorian proleptic, not Julian.
* doc/misc/calc.texi (Date Forms): Correct difference between Julian
Day and Rata Die.
* test/lisp/calc/calc-tests.el (calc-test-calendar): New test.
---
doc/misc/calc.texi | 4 ++--
lisp/calc/calc-forms.el | 38 ++++++++++++------------------------
test/lisp/calc/calc-tests.el | 21 ++++++++++++++++++++
3 files changed, 35 insertions(+), 28 deletions(-)
diff --git a/doc/misc/calc.texi b/doc/misc/calc.texi
index 75bbae58b2..c13ba8b940 100644
--- a/doc/misc/calc.texi
+++ b/doc/misc/calc.texi
@@ -11055,9 +11055,9 @@ Date Forms
is the numbers of days since 12:00 noon (GMT) on November 24, 4714 BC
in the Gregorian calendar (i.e., January 1, 4713 BC in the Julian
calendar). In Calc's scheme (in GMT) the Julian day origin is
-@mathit{-1721422.5}, because Calc starts at midnight instead of noon.
+@mathit{-1721424.5}, because Calc starts at midnight instead of noon.
Thus to convert a Calc date code obtained by unpacking a
-date form into a Julian day number, simply add 1721422.5 after
+date form into a Julian day number, simply add 1721424.5 after
compensating for the time zone difference. The built-in @kbd{t J}
command performs this conversion for you.
diff --git a/lisp/calc/calc-forms.el b/lisp/calc/calc-forms.el
index eb1a8248cd..71127ed779 100644
--- a/lisp/calc/calc-forms.el
+++ b/lisp/calc/calc-forms.el
@@ -585,29 +585,15 @@ math-absolute-from-gregorian-dt
"Return the DATE of the day given by the Gregorian day YEAR MONTH DAY.
Recall that DATE is the number of days since December 31, -1
in the Gregorian calendar."
- (if (eq year 0) (setq year -1))
- (let ((yearm1 (math-sub year 1)))
- (math-sub
- ;; Add the number of days of the year and the numbers of days
- ;; in the previous years (leap year days to be added separately)
- (math-add (math-day-in-year year month day)
- (math-add (math-mul 365 yearm1)
- ;; Add the number of Julian leap years
- (if (math-posp year)
- (math-quotient yearm1 4)
- (math-sub 365
- (math-quotient (math-sub 3 year)
- 4)))))
- ;; Subtract the number of Julian leap years which are not
- ;; Gregorian leap years. In C=4N+r centuries, there will
- ;; be 3N+r of these days. The following will compute
- ;; 3N+r.
- (let* ((correction (math-mul (math-quotient yearm1 100) 3))
- (res (math-idivmod correction 4)))
- (math-add (if (= (cdr res) 0)
- 0
- 1)
- (car res))))))
+ (when (zerop year) ; Year -1 precedes year 1.
+ (setq year -1))
+ (let* ((y (if (> year 0) year (+ year 1))) ; Astronomical year (with 0).
+ (y1 (- y 1))) ; Previous year.
+ (+ (* y1 365) ; Days up to the previous year...
+ (floor y1 4) ; ... including leap days.
+ (- (floor y1 100))
+ (floor y1 400)
+ (math-day-in-year year month day))))
(defun math-absolute-from-julian-dt (year month day)
"Return the DATE of the day given by the Julian day YEAR MONTH DAY.
@@ -618,7 +604,7 @@ math-absolute-from-julian-dt
(math-sub
;; Add the number of days of the year and the numbers of days
;; in the previous years (leap year days to be added separately)
- (math-add (math-day-in-year year month day)
+ (math-add (math-day-in-year year month day t)
(math-add (math-mul 365 yearm1)
;; Add the number of Julian leap years
(if (math-posp year)
@@ -712,11 +698,11 @@ math-format-date
(setcdr math-fd-dt nil))
fmt))))
-(defconst math-julian-date-beginning '(float 17214225 -1)
+(defconst math-julian-date-beginning '(float 17214245 -1)
"The beginning of the Julian date calendar,
as measured in the number of days before December 31, 1 BC (Gregorian).")
-(defconst math-julian-date-beginning-int 1721423
+(defconst math-julian-date-beginning-int 1721425
"The beginning of the Julian date calendar,
as measured in the integer number of days before December 31, 1 BC (Gregorian).")
diff --git a/test/lisp/calc/calc-tests.el b/test/lisp/calc/calc-tests.el
index 77d939eb40..e1ee20b5d2 100644
--- a/test/lisp/calc/calc-tests.el
+++ b/test/lisp/calc/calc-tests.el
@@ -193,6 +193,27 @@ calc-tests-simple
(let ((calc-number-radix 36))
(should (equal (math-format-number 12345678901) "36#5,O6A,QT1")))))
+(ert-deftest calc-test-calendar ()
+ "Test calendar conversions (bug#36822)."
+ (should (equal (calcFunc-julian (math-parse-date "2019-07-27")) 2458692))
+ (should (equal (math-parse-date "2019-07-27") '(date 737267)))
+ (should (equal (calcFunc-julian '(date 0)) 1721425))
+ (should (equal (math-date-to-gregorian-dt 1) '(1 1 1)))
+ (should (equal (math-date-to-gregorian-dt 0) '(-1 12 31)))
+ (should (equal (math-date-to-gregorian-dt -1721425) '(-4714 11 24)))
+ (should (equal (math-absolute-from-gregorian-dt 2019 7 27) 737267))
+ (should (equal (math-absolute-from-gregorian-dt 1 1 1) 1))
+ (should (equal (math-absolute-from-gregorian-dt -1 12 31) 0))
+ (should (equal (math-absolute-from-gregorian-dt -99 12 31) -35795))
+ (should (equal (math-absolute-from-gregorian-dt -4714 11 24) -1721425))
+ (should (equal (calcFunc-julian '(date -1721425)) 0))
+ (should (equal (math-date-to-julian-dt 1) '(1 1 3)))
+ (should (equal (math-date-to-julian-dt -1721425) '(-4713 1 1)))
+ (should (equal (math-absolute-from-julian-dt 2019 1 1) 737073))
+ (should (equal (math-absolute-from-julian-dt 1 1 3) 1))
+ (should (equal (math-absolute-from-julian-dt -101 1 1) -36892))
+ (should (equal (math-absolute-from-julian-dt -101 3 1) -36832))
+ (should (equal (math-absolute-from-julian-dt -4713 1 1) -1721425)))
(provide 'calc-tests)
;;; calc-tests.el ends here
--
2.20.1 (Apple Git-117)
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