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YearSpan

Function YearSpan( const ANow, AThen : TDateTime) : Double

Example​

procedure ScriptEvent(var Value: variant);
begin
  Value := YearSpan(EncodeDate(2020, 1, 1), EncodeDate(2021, 1, 1));
  // Value is approximately 1.002 because the interval is 366 days.
end;

Usage​

YearSpan returns an absolute fractional-year span using a 365.25-day divisor and Velox's raw numeric date/time difference.

Parameters

NameTypeDescription
ANowTDateTimeOne encoded date/time endpoint; it need not be later than AThen.
AThenTDateTimeThe other encoded endpoint.

Returns

A non-negative Double: the raw absolute day difference divided by 365.25.

Behaviour

For normal non-negative dates, the result is a fractional duration expressed in average four-year Gregorian years. Reversing the inputs does not change it.

Errors

The binding has no finite/range validation or exception handler. Invalid floating-point inputs and any resulting arithmetic failures are not normalised by Velox.

Additional Technical Info​

Returns an absolute fractional number of approximate years between ANow and AThen. One approximate year is 365.25 days. The function preserves fractions but uses Delphi's raw numeric TDateTime subtraction.

Implementation

Velox binds directly to System.DateUtils.YearSpan. The installed routine calls DaySpan, which compares and subtracts the raw Double values through SpanOfNowAndThen, then divides the result by the Delphi 37.0 ApproxDaysPerYear constant of 365.25. No timestamp conversion or calendar-field comparison occurs.

Edge cases and quirks

  • The value is approximate and does not describe completed anniversaries or exact calendar years.
  • Delphi's negative TDateTime representation stores the pre-30-December-1899 time fraction with a negative sign. Raw subtraction can therefore mismeasure intervals wholly before, or crossing, that epoch. YearsBetween uses timestamp-normalised chronology but discards fractions.
  • Binary floating-point rounding can put a result slightly above or below a mathematical boundary; avoid exact equality comparisons.
  • No timezone or daylight-saving adjustment occurs.

Performance and concurrency

The routine is constant-time floating-point arithmetic, allocation-free and independent of Velox shared state.

Related entries

  • YearsBetween — returns complete timestamp-normalised approximate years.
  • WithinPastYears — applies an inclusive limit to the complete-year result.
  • DaySpan — supplies the raw day span divided here.

External references

Created 2026-07-15