Account for leap year bug; fixes #264 #292
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hadley
approved these changes
Mar 13, 2017
src/utils.h
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| // If date is *prior* to the non-existent leap day: add a day | ||
| // If date is on the non-existent leap day: make negative and, in due course, NA | ||
| // Otherwise: do nothing | ||
| inline double removeLeapDay(double xlDate) { |
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I think this would be slightly easier to follow if you combined these two functions.
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Yes good point. Done 2d57d7a
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Thank you jennybc for making the change. |
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Excel reproduces a bug from Lotus 1-2-3: the non-existent leap day February 29, 1900 is included in the date system. This only affects sheets that use the 1900 date system and dates prior to March 1, 1900.
The proposed fix effectively removes that date. I adjust (increment) date-times on or before February 28, 1900. I convert date-times on February 29 1900 -- a day which does not actually exist -- to NA and throw a warning.
Since knowledge of the date system is now required for both the leap year adjustment and the offset, I store and pass the 1900 vs 1904 indicator around instead of the offset.
Fixes #264 and #148 (already closed as duplicate), if you want to read more about it.