The YEAR-TO-YYYY Function

The YEAR-TO-YYYY function converts argument-1, the two low-order digits of a year, to a four-digit year. Argument-2, when added to the year at the time of execution, defines the ending year of a 100-year interval, or sliding window, into which the year of argument-1 falls. The type of this function is integer.

General Format

    FUNCTION YEAR-TO-YYYY ( argument-1 [argument-2] )

Arguments

Argument-1 must be a nonnegative integer less than 100.
Argument-2 must be an integer.
If argument-2 is omitted, the function is evaluated as though 50 were specified.
The sum of the year at the time of execution and the value of argument-2 must be less than 10,000 and greater than 1699.

Returned Values

Maximum-year is calculated as follows:
(FUNCTION NUMVAL (FUNCTION CURRENT-DATE (1:4)) + argument-2)

where argument-2 of the NUMVAL function is the same as argument-2 of the YEAR-TO-YYYY function itself.
The equivalent arithmetic expression is:
1. When the following condition is true:
  FUNCTION MOD (maximum-year, 100) > = argument-1
  
  The equivalent arithmetic expression is:
  
  (argument-1 + 100 * (FUNCTION INTEGER (maximum-year/100)))
2. Otherwise, the equivalent arithmetic expression is:
  (argument-1 + 100 * (FUNCTION INTEGER (maximum-year/100) - 1))

Notes

In the year 1995, the returned value for FUNCTION YEAR-TO-YYYY (4, 23) is 2004. In the year 2008 the returned value for FUNCTION YEAR-TO-YYYY (98, (-15)) is 1898.
The YEAR-TO-YYYY function implements a sliding window algorithm. To use it for a fixed window, argument-2 can be specified as follows, where fixed-maximum-year is the maximum year in the fixed 100-year interval:
(fixed-maximum-year - FUNCTION NUMVAL (FUNCTION CURRENT-DATE (1:4)))

If the fixed window is 1973 through 2072, then in 2009 argument-2 has the value 63 and in 2019, the value 53.