Date conversions with a 360-day-year calendar

Abstract

Conversion of Gregorian calendar dates to dates of a 360-day-year calendar (i.e., a calendar having twelve months of 30 days each), and 360-day-year calendar dates to Gregorian calendar dates, are performed using a single three-column 367-entry conversion table. A search table unit searches the conversion table from the bottom upwards, i.e., a table search index is initialized to a value of 367, and decremented by unity each time a comparison is made and a match is not found. A first field in each row of the conversion table contains Gregorian leap year calendar days-of-the-year, a second field in each row contains Gregorian non-leap year calendar days-of-the-year, and a third field in each row contains 360-day-year calendar days-of-the-year. A graph of Gregorian days-of-the-year versus 360-day-year days-of-the-year has both vertical and horizontal sections. If a conversion from a Gregorian date stored in a month/day character register to a 360-day-year date is to be made, the field to be searched is dependent on the value of a flag is a leap year flag register. If a conversion from a 360-day-year date stored in a 360-day-year character register to a Gregorian date is to be made, after a match between the 360-day-year date and an entry in the third field is found the value of the flag in the leap year flag register determines which field the conversion day-of-the-year is taken from.