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F_DLST

IBExpert has developed its own simple internal function, to detect if the current timestamp is during European summer time or not.

Output Boolean True if current_timestamp is summertime, to be precise European Summer Time.

From Wikipedia:

"Daylight saving time (DST), also daylight savings time or daylight time (United States) and summer time (United Kingdom, European Union, and others), is the practice of advancing clocks during summer months so that evening daylight lasts longer, while sacrificing normal sunrise times. Typically, regions that use daylight saving time adjust clocks forward one hour close to the start of spring and adjust them backward in the autumn to standard time. In effect, DST causes a lost hour of sleep in the spring and an extra hour of sleep in the fall

"European Summer Time is the variation of standard clock time that is applied in most European countries (apart from Iceland, Georgia, Azerbaijan, Belarus, Turkey, and Russia) in the period between spring and autumn, during which clocks are advanced by one hour from the time observed in the rest of the year, in order to make the most efficient use of seasonal daylight. It corresponds to the notion and practice of daylight saving time to be found in many other parts of the world.

"In the EU, EFTA and associated countries, European Summer Time begins at 01:00 UTC/WET (02:00 CET, 03:00 EET) on the last Sunday in March and ends at 01:00 UTC (02:00 WEST, 03:00 CEST, 04:00 EEST) on the last Sunday in October each year; i.e. the change is made at the same absolute time across all time zones. European Union Directive 2000/84/EC makes the observance of summer time mandatory for EU member states (except overseas territories), though a proposal to repeal this directive and require that member states observe their own choice of time year-round from 2021 is currently going through the legislative process as of March 2019.

"Summer Time lasts, depending upon the calendar year, for either 30 or 31 weeks of the year. "

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