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(increment-calendar-month): Optionally handle systems without 12

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months per year (sync from trunk 2008-03-31; needed for above
holiday-bahai fix).
This commit is contained in:
Glenn Morris 2008-08-10 20:29:42 +00:00
parent f3f89619cf
commit 7b765ee622
2 changed files with 12 additions and 6 deletions
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4
lisp/ChangeLog
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@ -34,6 +34,10 @@
(calendar-absolute-from-bahai): Fix the leap-year case (sync from trunk
2008-03-20).
* calendar/calendar.el (increment-calendar-month): Optionally handle
systems without 12 months per year (sync from trunk 2008-03-31; needed
for above holiday-bahai fix).
* calendar/cal-islam.el (holiday-islamic): Doc fix (sync from trunk
2008-04-23).

14
lisp/calendar/calendar.el
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@ -1321,15 +1321,17 @@ with descriptive strings such as
(defconst lunar-phases-buffer "*Phases of Moon*"
"Name of the buffer used for the lunar phases.")
(defmacro increment-calendar-month (mon yr n)
(defmacro increment-calendar-month (mon yr n &optional nmonths)
"Increment the variables MON and YR by N months.
Forward if N is positive or backward if N is negative.
A negative YR is interpreted as BC; -1 being 1 BC, and so on."
`(let (macro-y)
A negative YR is interpreted as BC; -1 being 1 BC, and so on.
Optional NMONTHS is the number of months per year (default 12)."
`(let ((nmonths (or ,nmonths 12))
macro-y)
(if (< ,yr 0) (setq ,yr (1+ ,yr))) ; -1 BC -> 0 AD, etc
(setq macro-y (+ (* ,yr 12) ,mon -1 ,n)
,mon (1+ (mod macro-y 12))
,yr (/ macro-y 12))
(setq macro-y (+ (* ,yr nmonths) ,mon -1 ,n)
,mon (1+ (mod macro-y nmonths))
,yr (/ macro-y nmonths))
(and (< macro-y 0) (> ,mon 1) (setq ,yr (1- ,yr)))
(if (< ,yr 1) (setq ,yr (1- ,yr))))) ; 0 AD -> -1 BC, etc