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Fix date offset for countries that where on solar time in 1899 #38

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Fix date offset for countries that where on solar time in 1899 #38

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9 changes: 8 additions & 1 deletion bits/35_datecode.js
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Original file line number Diff line number Diff line change
Expand Up @@ -29,12 +29,19 @@ function parse_date_code(v/*:number*/,opts/*:?any*/,b2/*:?boolean*/) {
return out;
}
SSF.parse_date_code = parse_date_code;
function getTimezoneOffsetMS(date/*:Date*/)/*:number*/ {
// This function is a replacement for Date.getTimezoneOffset() which isn't
// precise enough for countries (like France, Russia or Spain) that were still on solar time in 1899
var time = date.getTime();
var utcTime = Date.UTC(date.getFullYear(), date.getMonth(), date.getDate(), date.getHours(), date.getMinutes(), date.getSeconds(), date.getMilliseconds());
return time - utcTime;
};
var basedate = new Date(1899, 11, 31, 0, 0, 0);
var dnthresh = basedate.getTime();
var base1904 = new Date(1900, 2, 1, 0, 0, 0);
function datenum_local(v/*:Date*/, date1904/*:?boolean*/)/*:number*/ {
var epoch = v.getTime();
if(date1904) epoch -= 1461*24*60*60*1000;
else if(v >= base1904) epoch += 24*60*60*1000;
return (epoch - (dnthresh + (v.getTimezoneOffset() - basedate.getTimezoneOffset()) * 60000)) / (24 * 60 * 60 * 1000);
return (epoch - (dnthresh + (getTimezoneOffsetMS(v) - getTimezoneOffsetMS(basedate)))) / (24 * 60 * 60 * 1000);
}